Federal Circuit Clarifies That Correcting Inventorship Cannot Undo Litigation Strategy: Implicit, LLC v. Sonos, Inc.

On March 9, 2026, the U.S. Court of Appeals for the Federal Circuit issued an important decision in Implicit, LLC v. Sonos, Inc., reaffirming that while patent inventorship can often be corrected retroactively under 35 U.S.C. § 256, those corrections do not erase procedural consequences when a party unduly delays raising the issue.

This decision serves as a reminder that inventorship issues should be addressed at the earliest possible opportunity not only during patent prosecution, but also before and during Patent Trial and Appeal Board (PTAB) proceedings.

Background

Implicit owned two patents directed to audio and networking technology. Sonos filed an inter partes review (IPR) before the PTAB to challenge the validity of the Implicit patents.  During the IPR proceeding, Sonos argued the Implicit patents were invalid as anticipated or obvious based primarily on an earlier-filed patent reference known as Janevski.

To avoid Janevski as prior art, Implicit argued the inventions had actually been conceived and reduced to practice before Janevski's filing date through the work of the named inventors and, importantly, an un-named inventor identified as engineer Guy Carpenter. The PTAB, however, concluded the evidence failed to establish that Carpenter's work legally inured to the benefit of the named inventors, meaning it could not be treated as their work for purposes of the inventorship analysis.  Accordingly, the Board upheld Janevski as invalidating prior art and held the challenged claims unpatentable.

A New Inventorship Theory—After the PTAB Decision

Following the PTAB's final written decisions and subsequent appeals, Implicit petitioned the USPTO to correct inventorship under 35 U.S.C. § 256 by adding Guy Carpenter as a named inventor. The USPTO granted the petitions and issued certificates of correction.

Implicit then argued because Carpenter had now been officially recognized as an inventor, the PTAB should reconsider its earlier decision regarding antedating the prior art.  More specifically, Implicit argued the correction of inventorship should be applied retroactively, which would mean Implicit’s invention predated the invalidating Janevski reference.

The Board disagreed, concluding that although § 256 corrections generally operate retroactively, Implicit had forfeited its ability to rely on this new inventorship theory because it failed to raise the issue during the original IPR proceedings.

The Federal Circuit Agreed

The Federal Circuit affirmed.

The court recognized that corrections of inventorship under § 256 generally have retroactive effect. However, the court emphasized that retroactivity does not eliminate ordinary procedural doctrines such as forfeiture.  In other words, correcting inventorship may change the patent's legal record, but it does not automatically allow a patent owner to reopen arguments that could have been made earlier.

The court explained that forfeiture occurs when a party fails to timely assert a right. Here, Implicit possessed the relevant inventorship information throughout the IPR proceeding yet chose to litigate based on a different theory. Only after receiving an unfavorable decision did it seek correction of inventorship. Under those circumstances, the court concluded the Board acted within its discretion in refusing to consider the new theory.

Distinguishing Prior Cases

Implicit relied heavily on the Federal Circuit's earlier decision in Egenera, Inc. v. Cisco Systems, Inc., where a mid-litigation correction of inventorship was permitted.

The Federal Circuit distinguished Egenera. In that case, a new claim construction fundamentally changed the scope of the asserted claims, creating a legitimate reason to reassess inventorship. By contrast, no comparable change occurred in Implicit. The relevant inventorship evidence had always been available to Implicit and nothing prevented it from seeking correction before the PTAB issued its final written decisions.

Practical Takeaways for Patent Owners

The decision provides several important lessons for patent applicants and patent litigants.

1. Verify inventorship early.

Inventorship should be carefully reviewed during patent preparation and prosecution. If questions arise later, they should be investigated promptly rather than waiting until litigation exposes a potential weakness.

2. Correct inventorship as soon as an issue is discovered.

Although § 256 provides a valuable mechanism for correcting inventorship, courts may still apply procedural doctrines—including forfeiture—if a party delays without adequate justification.

3. Litigation strategy matters.

Patent owners cannot assume they will receive a "second chance" to present a different inventorship theory after an adverse PTAB decision. Courts expect parties to present all available arguments when the issues are first litigated.

4. Retroactivity has limits.

The Implicit opinion reinforces an important distinction: retroactive legal effect and procedural timing are different concepts. A correction of inventorship may relate back to the original patent, but it does not necessarily revive litigation positions that have already been forfeited.

Why This Decision Matters

The Federal Circuit's opinion reinforces an increasingly important principle in PTAB practice: parties must litigate efficiently and completely the first time. While patent law provides mechanisms to correct genuine errors, including inventorship mistakes, those mechanisms do not excuse strategic delay or allow parties to withhold arguments until after an unfavorable outcome.

For patent owners, the safest approach is to evaluate inventorship carefully before enforcement, before filing an IPR response, and certainly before final written decisions are issued. Early diligence may preserve substantive rights that cannot later be recovered through procedural corrections.