Gygax/TSR went so far as to claim that Advanced D&D was a different game from D&D to not have to pay Dave Arneson royalties on any of the releases. Arneson sued

Gygax/TSR went so far as to claim that Advanced D&D was a different game from D&D to not have to pay Dave Arneson royalties on any of the releases. Arneson sued TSR multiple times and they settled out of court, granting him royalties on AD&D: https://en.wikipedia.org/wiki/Dave_Arneson#After_TSR https://en.wikipedia.org/wiki/Dave_Arneson#After_TSR