Gideon Korrell Shares Why PTAB Fact Findings Don’t Bind District Courts

In October 2025, the Federal Circuit overturned a district court ruling in Inland Diamond Products Co. v. Cherry Optical Inc. The court made one point very clear: findings made by the Patent Trial and Appeal Board (PTAB) do not automatically control what happens later in the district court when patent validity is challenged.

As Gideon Korrell explains, the decision confirms that PTAB cases and district court cases follow different legal rules, especially when it comes to how much proof is required.

Background of the Dispute

The case involved two related patents owned by Inland Diamond Products. Earlier, those patents were challenged in inter partes review (IPR) proceedings at the PTAB. The Board ruled that several main claims were unpatentable because they were obvious. However, it did not invalidate certain dependent claims.

Later, Inland sued Cherry Optical in district court, relying on those dependent claims. Cherry had not been involved in the earlier IPRs. Even so, Cherry asked the district court to rule the patents invalid without a trial, arguing that Inland could not dispute factual issues already decided by the PTAB.

The district court agreed and granted summary judgment. On appeal, the Federal Circuit disagreed.

The Core Legal Issue: Different Standards of Proof

The key problem was that the PTAB and district courts use different standards of proof:

• PTAB: A patent can be found unpatentable if it is more likely than not invalid.
• District court: A patent can be invalidated only if invalidity is proven clearly and convincingly.

The Federal Circuit explained that facts found under a lower standard cannot automatically be used in a setting where a higher standard applies. Even if the PTAB found something persuasive, that does not mean the same fact has been proven strongly enough for the district court.

Gideon Korrell points out that this difference protects the basic rule that patents are presumed valid unless strong evidence proves otherwise.

Why Issue Preclusion Failed Here

Issue preclusion applies only when the same issue was already decided under the same legal rules. That was not the case here.

By relying on PTAB findings, the district court allowed Cherry to avoid proving invalidity under the higher district court standard. This wrongly shifted the burden away from Cherry and limited Inland’s ability to defend its patents.

The Federal Circuit said that the approach was improper. Cherry still had to prove invalidity using evidence presented in the district court.

Claim Construction Creates Another Barrier

There was another important issue: claim interpretation.

Because the IPRs were filed before November 2018, the PTAB used a broader way of reading patent claims. District courts use a narrower approach. This means the same claim language may be understood differently in each forum.

The Federal Circuit noted that these differences alone can prevent issue preclusion. Gideon Korrell highlights that this often matters in older IPR cases that return to the district court years later.

Survival of IPR Does Not Decide the Case

The district court seemed to assume that because the claims survived the IPRs, it affected how validity should be judged later. The Federal Circuit rejected that idea.

Whether claims survived IPR, were never challenged, or were only partly reviewed does not matter. Unless a claim has been finally ruled invalid on appeal, it remains valid in the district court and keeps its legal protections.

What the Decision Means Going Forward

The Federal Circuit sent the case back to the district court with clear instructions. If invalidity is found, it must be based on district court evidence, not PTAB issue preclusion. Summary judgment is still possible, but only if no reasonable jury could find the patent valid under the clear-and-convincing standard.

The takeaway is simple: PTAB findings cannot replace a full invalidity case in district court. As Gideon Korrell explains, parties must meet the proper burden of proof in the proper forum with the proper evidence.