The Federal Circuit’s recent decision in Implicit, LLC v. Sonos, Inc., No. 25-853 (Fed. Cir. Mar. 9, 2026), addresses a procedural question that arises occasionally in patent litigation but rarely receives sustained appellate attention: what happens when a patent owner corrects inventorship after a Patent Trial and Appeal Board (PTAB) final written decision?
The short answer from the court: a certificate of correction under 35 U.S.C. § 256 does not give a patent owner a second chance to make arguments that could have been raised earlier in the inter partes review (IPR). Even though inventorship corrections are generally retroactive, the Federal Circuit held that ordinary procedural doctrines—particularly forfeiture—still apply.
The decision reinforces an important principle about IPR practice: patent owners must present all viable arguments during the proceeding itself. Post-hoc attempts to change the evidentiary landscape will not reopen the record.
Background of the Dispute
The case arose from IPR petitions filed by Sonos challenging two patents owned by Implicit: U.S. Patent Nos. 7,391,791 and 8,942,252. The patents relate to wireless audio systems—technology that sits squarely within the ecosystem where companies like Sonos have built significant commercial products.
The key prior art reference relied upon by Sonos was a patent issued to Janevski. Because Janevski had a filing date of December 2001, Implicit attempted to antedate the reference by arguing earlier conception and reduction to practice.
The strategy depended on showing that two named inventors conceived of the invention and communicated it to an engineer who helped implement the system. If that work properly “inured to the benefit” of the inventors, then the reference might not qualify as prior art.
The PTAB rejected the argument. It found the evidence insufficient to establish conception and communication of the invention before the Janevski filing date. As a result, the Board determined that Janevski qualified as prior art and that the challenged claims were unpatentable as anticipated or obvious.
The Complication: Arthrex and a Procedural Reset
The case took an unusual procedural path because it intersected with the constitutional litigation surrounding PTAB administrative patent judges.
After the Federal Circuit issued its decision in Arthrex, Inc. v. Smith & Nephew, Inc., the appeal was remanded so that the patent owner could seek review by the Director of the USPTO. The Supreme Court later confirmed the Director-review remedy in United States v. Arthrex, Inc.
While that process unfolded, Implicit made a strategic move.
It asked the USPTO to correct inventorship on both patents to add a third individual—Guy Carpenter—who had previously been described only as an engineer involved in implementation.
The USPTO issued certificates of correction adding Carpenter as an inventor.
Implicit then attempted to rely on those corrections to revisit the PTAB’s earlier findings about conception and reduction to practice.
The PTAB’s Decision on Remand
The Federal Circuit remanded the case to the Board for a narrow question: what effect, if any, should the inventorship corrections have on the original final written decisions?
The Board concluded that the corrections did not change the outcome.
Although § 256 corrections typically operate retroactively, the Board determined that equitable doctrines—particularly waiver and judicial estoppel—prevented Implicit from relying on the newly corrected inventorship at that stage of the proceedings. Implicit appealed again.
The Federal Circuit’s Holding
The Federal Circuit affirmed, framing the issue as a narrow but important procedural question: whether the retroactive effect of an inventorship correction under § 256 eliminates the possibility that a party forfeited arguments by failing to raise them during the IPR. The answer was no.
The panel held that the retroactive effect of § 256 does not override ordinary procedural doctrines such as forfeiture.
In other words, a patent owner cannot rely on a later correction of inventorship to resurrect arguments that were not properly presented during the IPR itself.
This was a matter of litigation procedure, not patent validity doctrine.
The Federal Circuit therefore upheld the Board’s determination that Implicit forfeited the argument by waiting until after the final written decisions to correct inventorship and raise new theories tied to that correction.
Why Retroactivity Did Not Control
Implicit’s core argument was that § 256 corrections operate retroactively. Historically, courts have treated corrected inventorship as though the patent had always listed the proper inventors.
The Federal Circuit did not dispute that principle.
However, the court emphasized that retroactivity in substantive patent law does not automatically displace procedural rules governing litigation conduct.
A correction may retroactively fix inventorship for purposes of ownership or validity analysis, but it does not erase the procedural reality that the issue was not raised in the IPR record.
The court therefore treated the case as a straightforward application of forfeiture doctrine.
Relationship to Earlier Inventorship Case Law
The decision fits within a line of Federal Circuit cases addressing inventorship corrections and their litigation consequences.
For example, Pannu v. Iolab Corp. recognized that incorrect inventorship can render a patent invalid unless corrected under § 256. The statute was designed to prevent harsh outcomes when errors occur.
Similarly, in Egenera, Inc. v. Cisco Systems, Inc., the Federal Circuit examined whether a patent owner could remove an inventor during litigation in order to avoid prior art complications. That case also highlighted the strategic consequences of inventorship corrections.
What Implicit v. Sonos adds is a procedural dimension: even if a correction is legally effective, it cannot be used to reopen issues that should have been addressed earlier in the administrative proceeding.
As Charles Gideon Korrell notes, the case illustrates how procedural doctrines can effectively limit the practical impact of otherwise powerful statutory remedies.
The Importance of IPR Record Building
From a practical perspective, the decision underscores the importance of developing the factual record during the IPR itself.
Inventorship questions often intersect with priority arguments, particularly when a patent owner seeks to antedate prior art.
If a third party’s work is critical to establishing conception or reduction to practice, the inventorship issue should be addressed early—either through correction proceedings or through the evidentiary record presented to the PTAB.
Waiting until after the Board issues a final written decision risks precisely the outcome seen here.
Charles Gideon Korrell believes that the ruling will likely encourage patent owners to scrutinize inventorship more carefully before entering IPR proceedings, particularly where earlier development work involved engineers or collaborators who were not originally listed as inventors.
Implications for Patent Owners
The case sends several signals to patent owners defending patents in PTAB proceedings.
First, inventorship corrections remain available and can still have substantive legal consequences.
But second—and more importantly—the timing of those corrections matters.
If inventorship is central to priority or conception arguments, the issue must be addressed during the IPR. Courts are unlikely to permit a late correction to alter the evidentiary posture of a completed proceeding.
As Charles Gideon Korrell observes, the Federal Circuit’s reasoning reflects a broader theme in PTAB jurisprudence: the administrative process is designed to produce a closed record, and parties are expected to present their full case within that framework.
Implications for PTAB Practice
The decision also reflects the Federal Circuit’s continued emphasis on procedural discipline in PTAB litigation.
Over the past decade, the court has repeatedly reinforced doctrines such as waiver and forfeiture in the context of IPRs. Arguments not raised before the Board generally cannot be raised later on appeal.
By applying forfeiture even in the face of a retroactive statutory correction, the court signaled that those procedural constraints remain robust.
The PTAB process is not designed to allow iterative relitigation after the fact.
Conclusion
Implicit v. Sonos provides a clear reminder that statutory tools like § 256 corrections cannot override the procedural realities of patent litigation.
Even though inventorship corrections operate retroactively, they do not reopen a closed administrative record or undo arguments that were forfeited during the original proceeding.
For patent owners involved in IPRs, the lesson is straightforward: issues related to inventorship, conception, and priority must be addressed early and thoroughly. Waiting until after a final written decision to adjust the theory of the case is unlikely to succeed.
By affirming the PTAB’s decision, the Federal Circuit reinforced the importance of procedural finality in inter partes review—an outcome that will likely shape how inventorship disputes are handled in future PTAB litigation.