Good point about "vintage"; I hadn't considered the usual standards of the label. But if they're also describing a show that was never recorded, that's not much of a hint--such shows disappear so thoroughly that few people have any idea who was in the cast.
"What's the next vintage musical we'll be recording? Hint #1: one of the supporting players later recurred on two top-rated sitcoms."
It's confusingly worded, but assuming this refers to the cast of the original production, Ernie Sabella had recurring roles on Perfect Strangers and That's So Raven after The Robber Bridegroom.