On February 7, 2012, the US Court of Appeals for the Federal Circuit issued an opinion in Adair v. Carter clarifying when a party may rely on a post-critical date patent claim to declare an interference.

Section 135(b)(1) of the Patent Act allows a claim to be copied from an issued patent and submitted in a pending patent application to provoke an interference between the patent and application only if the claim is copied before one year from the patent grant date (critical date). Claims submitted in the application after the critical date are generally barred from use as a basis for declaring an interference except in the limited situation where the applicant already claimed substantially the same invention as the patentee before the critical date. Adair, the party seeking the interference declaration, filed Claim 24 after the critical date but argued that Claim 24 fell within the exception based on certain pre-critical date claims.

The Federal Circuit upheld the Board of Patent Appeals and Interferences' findings that the pre-critical date claims did not allow Claim 24 to be a basis for the interference declaration because Claim 24 and the earlier claims were materially different on the basis that:

This case highlights that patent claims filed after the critical date can only be used to declare an interference in narrow circumstances where the post-critical date patent claims are not materially different from the pre-critical date claims. The applicant should avoid putting limitations in pre-critical date claims if it may rely on these as a basis to declare an interference with post-critical date claims.