Federal Circuit: Unreachable Coinventor = Invalid Patent—Strict Construction of 35 U.S.C. Section 256(b) in Fortress Iron v. Digger Specialties

The U.S. Court of Appeals for the Federal Circuit solidified patent law on April 2, 2026: when a coinventor cannot be located, patents bearing an inventorship omission are invalid. The decision in Fortress Iron, LP v. Digger Specialties, Inc. makes clear that failure to satisfy 35 U.S.C. Section 256(b)’s requirements constitutes an incurable defect.

The facts were straightforward. Fortress Iron owned U.S. Patents 9,790,707 and 10,883,290 covering a vertical cable rail barrier system. Two Fortress employees and two employees of a quality-control liaison firm, Quan Zhou Yoddex Building Material Co., Ltd (YD), had jointly conceived the inventions. During litigation, Digger Specialties identified the YD employees—Hua-Ping Huang and Alfonso Lin—and demanded their addition as coinventors.

Fortress attempted correction under Section 256(a). Lin could be added; Huang could not be located. Here is where Section 256(b) becomes critical: it mandates notice to all “parties concerned” and an opportunity to be heard. Huang’s disappearance rendered compliance impossible.

The Federal Circuit held the patents invalid. The court’s reasoning was strict constructionist: Section 256 requires notice to all parties concerned regardless of whether correction would be “non-prejudicial” in other respects. If an omitted coinventor cannot be found, and therefore Section 256(b) cannot be satisfied, the patent is simply invalid. This constitutes significant precedent.

The implications for practice are substantial. First: inventorship accuracy at the time of filing is now demonstrably critical. Collaborative projects and post-acquisition inventor verification require rigorous documentation. Second: portfolio audits must systematically examine inventorship fidelity as a standard due-diligence item. Litigation exposure hinges on it.

The ruling extends internationally. PCT filings and national phase entries sometimes carry divergent inventorship data. Multinational R&D operations must maintain strict inventorship-chain consistency. A mismatch invites post-examination challenges in any jurisdiction that applies similar statutory requirements.

Fortress Iron illustrates a hard truth about patent law: administrative precision governs. Technological merit and commercial value matter little if foundational formalities collapse. Inventorship accuracy is now understood as integral to asset protection, not a documentation afterthought.