I would bill all the kids that were in the movie first due to squater's rights
Shorosky would get billing after the actors from the movie.
Then the new actors would get billed
I would save Lydia's billing for last with a "and starring...as"


Fame

Starring
Erica Gimpel as Coco (She is the flagbearer)
Lee Cuerri as Bruno
Gene Anthony Ray as Leroy
Lori Singer as Julie (I pushed her to 4th billing because she was prominent)
Albert Hague as Shorosky
Valerie Lansburg as Doris
P.R. Paul as Montgomery
Carol Jenkins as Sherwood
Carlo Imperato as Danny
and Starring Debbie Allen as Lydia

You guys do your own billing listing and it could be from any season.