vc-version-backup-file

vc-version-backup-file is an autoloaded compiled Lisp function in `vc.el'.

(vc-version-backup-file FILE &optional REV)

Return name of backup file for revision REV of FILE.
If version backups should be used for FILE, and there exists
such a backup for REV or the working revision of file, return
its name; otherwise return nil.