I cant answer your question honestly, but I do have my opinions. I think Ringo probably has to have an OK from Yoko, Paul, or George's estate depending on the song, as well as the record label that owns the rights. As for the Beatles sides of it all, I dont think they really ever deny Ringo due to his good nature and the fact that he really doesnt sell a ton of albums (shame really as I love his stuff). The record companys, on the other hand, take their fair share i'm sure.
