In the common law, res judicata (the thing that was decided) applies to a situation where a final judgement has been made, yet a party is trying to re-litigate the same case. Res judicata maintains the previous judgement and avoids repetition, thus preserving the effect of the first judgment.

Res judicata is also applicable in prosecution before the USPTO. MPEP § 2190 discusses the issue and explains how the USPTO views the doctrine:

A patent owner or applicant may be precluded from seeking a claim that is not patentably distinct from a claim that was previously rejected if the rejection was affirmed on appeal and the decision on appeal became final. A res judicata rejection should be applied only when the earlier decision was a decision of the Patent Trial and Appeal Board (or its predecessor Board) or any one of the reviewing courts and when there is no opportunity for further court review of the earlier decision. See In re Hitchings, 342 F.2d 80, 85, 144 USPQ 637, 641 (CCPA 1965) (holding that unappealed rejections from examiners cannot have a preclusive effect).

There are, of course, exceptions to this rule, including when an applicant has “new evidence.” In re Herr, 377 F.2d 610, 153 USPQ 548 (CCPA 1967) (res judicata not applicable despite similarities between previously adjudicated and current claims because applicant provided new evidence of patentability).

Despite the clear exceptions, USPTO examiners can sometimes take the broad statements in the MPEP as gospel and refuse to consider that an exception may apply. An example is appeal 2022-003276, Application 15/090,845. Here, the applicant had previous lost an appeal (where the claims were rejected as failing written description and enablement) and had come back with additional evidence (the citation of a new paper). The examiner applied the rejection as follows:

T]he decision by the Patent Trial and Appeal Board, of October 29, 2020, affirmed the . . . [35 U.S.C. §] 112(a) written description and enablement rejection[s] of the claims with respect to the unbounded bypass ratio. Under the principles of Res judicata, the claims are not appealable.

The Applicant went back to the Board and argued that that res judicata is not applicable to the present claims because they submitted new evidence (a technical report). Specifically, the applicant pointed to MPEP § 2190 and cited In re Herr, 377 F.2d 610 (CCPA 1967) and In re Russell, 439 F.2d 1228 (CCPA 1971), both holding that “res judicata [was] not applicable despite similarities between previously adjudicated and current claims because applicant provided new evidence of patentability”. The Board agreed, finding:

We find Appellant’s argument persuasive. In Herr, the claims in the original appeal were identical to the claims in the later appeal, but Appellant submitted new evidence of patentability in the later appeal.

While the applicant here was successful in overcoming the issue of res judicata, they were ultimately unsuccessful on the substantive issues because the new evidence submitted was dated after their priority date.

So, even if your appeal is at first rejected by the PTAB and new evidence is available that might alter the decision, res judicata should not act as a procedural block.