For years, it was an underappreciated wrinkle in the historic deal that merged the established National Basketball Association and the upstart American Basketball Association in 1976. The owners of the Spirits of St. Louis agreed to be paid a small fraction of the N.B.A.’s television money to comfort them for being cut out of joining the older league.

Their piece amounted to a sliver of the modest amount that CBS was paying the N.B.A. in those days. But if the share was small then, one particular term of the arrangement was attractive: the owners, Ozzie and Daniel Silna, would be paid the money every year in perpetuity, or as long as the N.B.A. existed.

The Spirits became a distant memory, even for people in St. Louis. But the N.B.A. has continued to exist quite nicely, meaning the Silnas’ haul has been substantial: $255 million and counting. But as sweet as the deal has been, the Silnas want more, and they have gone to court to get it.

In Manhattan federal court on Thursday, lawyers for the Silna brothers and the league argued over whether the men are owed money beyond what they get from the N.B.A.’s national broadcast and cable television contracts. They want to tap into the money the league gets from international broadcasts, NBA TV, the league’s cable network, and other lucrative deals that could not have been imagined in the three network television universe of 1976.