I did see some episodes of Bill Cullen on MG-HS Hour, where he was introduced just like Matt had assumed. I would imagine he played the first half each day, and if not, somebody on the bottom row may have let Bill take his/her seat, and moved up to the top row. There were two other celebrities who were introduced but did not walk onto the stage setting. One was George Gobel (maybe vision problems, I don't know for sure), and David L. Lander, who was in the early stages of Multiple Sclerosis (according to a People magazine article years later).