“This case began in 1924” is not something you expect to see in an opinion published anytime recently. But the Ninth Circuit just issued an opinion with precisely that phrase, illustrating one instance where preclusion doesn’t apply to bar new claims.

In 1924 the United States filed suit in Nevada federal court to establish the water rights of the Walker River Paiute Tribe. In 1940 the district court finalized a decree governing the water rights and retaining jurisdiction. Fifty-two years later, the Tribe filed counterclaims asserting new rights and spawning a round of litigation that lasted until 2015.

After briefing on Rule 12(b) jurisdiction issues—but without any briefing on preclusion—the district court sua sponte dismissed the Tribe’s claims on claim preclusion grounds. The Tribe and the United States appealed, and the Ninth Circuit reversed.

The Ninth Circuit first held that the claims asserted in the 1990s were not “a new action.” The District Court reasoned that because the claims were assigned to a “subfile” they were distinct from the original case. The Ninth Circuit rejected this logic, noting that “designating a subfile . . . logically means that the contents are part of the larger case and not an entirely new action.” And none of the parties had argued that slotting the new claims into a subfile meant they were “a new action.”

The Ninth Circuit proceeded to make short work of the preclusion question: “This circuit has never ‘upheld a dismissal for claim or issue preclusion where the parties were not given any opportunity to be heard on the issue,’ and we decline to do so here.” What’s more, during the round of Rule 12(b) briefing “the district court explicitly told the parties not to brief [claim preclusion] issues, before dismissing on that ground.” The Ninth Circuit remanded with instructions that the district court must put any claim preclusion analysis through “the rigors of the adversarial process.”

Here is the Ninth Circuit’s opinion.