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Rule 26(e) Supplementation of Expert Reports: Not as Easy as It May Look

Paul M Kessimian and Daniel Marran


  • This article examines what to do and what to consider when the usual precautions litigators take with expert witnesses do not work.
  • It is a summary overview of the often competing considerations and the many potential pitfalls that may factor into the decision to supplement or amend an expert report pursuant to Federal Rule of Civil Procedure 26(e)(2).
Rule 26(e) Supplementation of Expert Reports: Not as Easy as It May Look
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When to Supplement, When You Might Not, and What to Consider

Expert testimony plays a critical role in our cases. We painstakingly screen candidates to identify the right expert for the engagement, diligently stress-test our chosen expert’s opinions and asserted bases, and exhaustively prepare experts for the attacks likely to be issued by the other side—all with the end goal of ensuring that proffered opinions are well supported, well explained, and, ultimately, persuasive to a lay jury. Each of those steps is of course itself the subject of countless practice tips and case law surveys.

This article skips ahead and instead examines what to do and what to consider when those precautions do not work—when, despite the lawyer’s best efforts, the expert report has a problem. Perhaps the initial expert report contained plain errors in calculation. Perhaps deposition questioning from opposing counsel obtained an admission that your expert did not evaluate evidence, which appears to undermine the expert’s conclusions. What are the types of questions one should ask in deciding what to do next? What analysis flows from those questions? What are the costs, benefits, and risks to consider when charting a course after one becomes aware of a problem with the expert’s report? What follows is a summary overview of the often competing considerations and the many potential pitfalls that may factor into the decision to supplement or amend an expert report pursuant to Federal Rule of Civil Procedure 26(e)(2).

The Rules

We start, perhaps obviously, with the rules. Rule 26(e) requires parties to timely supplement or correct a disclosure “if the party learns that in some material respect the disclosure or response is incomplete or incorrect, and if additional or corrective information has not otherwise been made known to the other parties during the discovery process or in writing.” Fed. R. Civ. P. 26(e)(1)(A). The rule expressly extends to both expert reports and expert deposition testimony. Fed. R. Civ. P. 26(e)(2).

At first blush, one may think the rule looks like a get-out-of-jail-free card. After all, by its terms, it requires supplementation of materially “incomplete” or “incorrect” disclosures. So, if an expert’s report or opinions are “incomplete” or “incorrect,” especially after those questions are raised in a deposition, does the rule give parties a risk-free “do-over”? According to courts interpreting the rule, the answer is no.

First, courts have repeatedly emphasized that Rule 26(e) is not a license to improve upon an expert’s initial effort. The rule “does not permit supplementation of an expert report to remedy an inadequate or incomplete preparation or review by an expert in the first instance.” Covington v. Memphis Publ’g Co., No. 05-2474-DV, 2007 WL 9710110, at *3 (W.D. Tenn. July 27, 2007), adopted by 2007 WL 4615978 (W.D. Tenn. Oct. 16, 2007). It does not countenance supplements “intended to ‘deepen’ or ‘strengthen’ [an] expert’s prior Rule 26(a)(2)(B) report.” Guidance Endodontics, LLC v. Dentsply Int’l, Inc., 2009 WL 3672373, at * 11 (D.N.M. 2009) (citation omitted). It certainly does not “give license to sandbag one’s opponents with claims and issues which should have been included [in the report].” Bd. of Cty. Comm’rs v. Freeport-McMoran Copper & Gold, Inc., 2013 WL 7802171, at *1 (Sept. 5, 2013) (internal quotes omitted).

In short, to summarize a rich vein of similar opinions, many courts have limited patience for attempts to use Rule 26(e)(2) for “fixes” that could have been addressed in the original report (and thus within the applicable scheduling order deadlines). The general attitude makes sense. Doing otherwise risks “wreak[ing] havoc in docket control and amount[ing] to unlimited expert opinion preparation.” Martinez v. Costco Wholesale Corp., 336 F.R.D. 183, 189 (S.D. Cal. 2020) (citation omitted).

Second, it is worth noting—separate from the above timing considerations—that the rule imposes its own default deadline: Rule 26(e) supplementation must be made “by the time the party’s pretrial disclosures under Rule 26(a)(3) are due.” Fed. R. Civ. P. 26(e)(2). Accordingly, it would appear that, notwithstanding scheduling order deadlines for initial expert disclosures and rebuttals, supplementation mandated by Rule 26(e)(2) is timely until the deadline for pretrial disclosures.

Some decisions support this view. See Whitesell Corp. v. Whirlpool Corp., 2010 WL 1611361, at *1 (W.D. Mich. 2010) (“[T]he timeliness of Mr. Bero’s final report depends on whether it supplements his original report [under Rule 26(e)(2)] or whether it conveys entirely new opinions that should have been submitted at least 90 days before trial under Rule 26(a)(2)(C).”) But other courts have suggested to the contrary that Rule 26(e)(2) presents only a default deadline in the absence of a scheduling order governing expert disclosure. For these courts, supplementation must be both “timely” pursuant to Rule 26(e)(1)(A) and submitted prior to the Rule 26(e)(2) deadline. See Aileron Inv. Mgmt., LLC v. Am. Lending Ctr., LLC, 2022 WL 523549, at *2 (M.D. Fla. Feb. 22, 2022) (“The extent to which an expert’s supplement is deemed ‘timely’ under Rule 26(e) is generally tied to the discovery and expert disclosure deadlines set forth in a court’s scheduling order, although—absent a directive from the court to the contrary—Rule 26(e) permits Rule 26(a)(2)(B) expert witnesses to supplement their disclosures up until the pretrial disclosure deadline.” (citation omitted)).

In any event, further parsing of the deadline language has limited utility. Practically speaking, supplementation (or, at least, difficult questions over whether to supplement) will arise after the expiry of the court’s expert disclosure deadlines. Whether a supplement requires the court’s permission and good cause (upon a motion for leave to exceed scheduling order deadlines) or merely the court’s blessing as proper Rule 26(e) supplementation (upon a motion to exclude filed by the other side), many of the same considerations are likely at play.

What to Think about When You Think about Supplementation

The benefits and costs of Rule 26(e) supplementation implicate a variety of different, often competing factors. While the significance of any given factor may wax or wane depending on the circumstances of the case, certain questions predominate. Moreover, courts have substantial discretion in handling discovery disputes—and their own calendars. That said, the following questions provide a framework for how to think about supplementation.

1. Does the supplemental opinion evaluate new evidence that was unavailable at the time of the initial report?

A critical threshold question is whether the supplementation is predicated on “new evidence.” After all, Rule 26(e)(2) supplementation is limited to “incomplete” or “inaccurate” disclosures. Courts are generally more willing to consider requests to supplement—at least in the absence of uncurable prejudice to the other side—where the supplementation opinions could not have been reached based on the evidence available at the time of the original report. See, e.g., Aileron, 2022 WL 5234549, at *3 (granting leave to supplement damages opinion where dollar amounts of offsetting settlement payments were unavailable at the time of original report).

In contrast, courts generally express limited patience where the evidentiary predicate for the supplemental opinion was available, but not reviewed by the expert, at the time of the original report. As noted above, courts have expressed in myriad ways that parties are out of luck when the expert’s prior report merely overlooked or understated the import of then available evidence.

The tactical takeaway is that any effort to supplement should (if at all possible) be framed in terms of newly available evidence or information. In evaluating supplementation, attorneys should understand from the outset that supplemental reports may be doomed to exclusion if there is no new information prompting the effort.

2. Does the “supplementation” effect a significant change in the expert’s proffered opinions?

On its face, the rule does not appear to bar a Rule 26(e)(2) supplementation that substantially alters the expert’s original opinions. It is at least conceivable that changes required to amend an “incomplete or incorrect” disclosure might effect a substantial change to the expert’s original opinion.

In practice, significant departures from the original opinions are likely to be found either outside the scope of Rule 26(e)(2) entirely or to be excluded due to unfair prejudice, timeliness, or other scheduling or efficiency-adjacent reasons. And, of course, even if supplementation is permissible, a 180-degree course correction by an expert is likely to be exploited by the other side at trial.

3. What is the risk of exclusion absent supplementation?

The risks of not supplementing must be part of any analysis as to the benefits and drawbacks of a supplemental report. A key consideration is whether supplementation obviates a colorable motion for exclusion. Is testimony on this evidence or topic or opinion likely to be held inadmissible absent a supplement? If so, even a supplemented report that faces a high likelihood of exclusion may nonetheless be worth filing. The alternative is a meritorious Daubert challenge.

4. Where are you in the case schedule?

Notwithstanding compliance with Rule 26(e)(2)’s default deadline, the court is likely to take a dim view of supplementation that takes a wrecking ball to the scheduling order. In light of this practical reality, sooner is, of course, better. The decision to pursue supplementation should be made quickly, as soon as any defect is identified.

5. Is further discovery needed to cure potential prejudice to the other side?

Courts are unlikely to deny the other side an opportunity to respond to the supplemented opinion. This may require, at minimum, a second deposition of your expert. It may also require an opportunity for your opponent’s expert to serve a supplemental rebuttal. Further still, if an adequate response requires reopening fact discovery, the cost to do so (leaving aside the court’s likely receptivity to such a proposal) needs to be taken into account. In short, is the supplemental opinion worth the hassle its service will occasion?

6. How does your opponent stand to benefit from a reciprocal opportunity to supplement?

Similarly, it is prudent to assume your opponent will be given a reciprocal opportunity to supplement. Is the benefit of your expert’s supplemental opinions outweighed by “points” your opponent might score in response? Are there holes in your opponent’s expert reports that might be rectified by similar supplementation?

Taking It All Together—Do the Benefits Outweigh the Risks?

Absent a scenario in which one particular factor overrides other considerations—for instance, a likely meritorious, case-dispositive Daubert challenge absent supplementation—there may very well be reasonable arguments both for and against supplementation pursuant to Rule 26(e)(2). What is one to do?

The evidentiary and persuasive benefits to your case on the merits must be weighed against the opportunity for the other side to strengthen its own opinions. Even if that factor weighs in favor of attempting to supplement, one must consider the possibility that the supplementation is excluded as discussed above. This exercise is likely to be expensive due to the work on the supplementation itself, any subsequent motion practice if the opponent seeks to exclude, the review of and response to an opponent’s own supplementation, and any additional expert depositions or other related discovery. In essence, does the incremental increase in likelihood of success on the merits outweigh the risks, time, and increased litigation costs associated with the supplementation?

The questions and factors surveyed in this article may not yield an obvious answer. Often, the multifactor analysis previewed here may persuade you only that both supplementation and a failure to supplement would run significant risks. Nevertheless, the questions and factors surveyed above provide the practical guideposts (informed by the law) to reach an informed decision.