Is there a source by which to identify the administrator of rights for the works of a deceased choreographer?

I am specifically interested in finding the administrator of rights for the choreography of William Dollar, but a general source would be very useful. I have tried the New York Public Library's very fine Performing Arts Library, but they are unable to help with this question.

well he died in 1986. the library's catalogue contains a brief mention of a performance of a ballet of his by the state ballet of missouri in 1988. i guess they would have had to obtain permission so as that was after his passing, maybe they would know.

Pennsylvania Ballet might know. Former faculty member, Yvonne Patterson did inherit the rights to his work. Mr. Dollar passed away in Philadelphia. Jeffrey Gribler, ballet master, did remain very close to Mrs. Patterson. Mrs. Patterson did not attend the Weisberger 80th party in October, so I am assuming she is not in good health. They were/are both lovely people.