Look. It is a cartoon and anything is possible but I still decided (just for fun!) to cook up an explanation. Here is my explanation. They ran a projector for some of the scenes. When Scrooge watches a younger version of himself sitting with his girlfriend Belle he is actually looking at a projected film of the two and the lady who played Belle is not actually in the playhouse theater at the time. To give just one example. This is in the shorter version of the special. In the longer version we see Magoo and some of the play's other actors taking bows after the curtain goes down with the play's climax finale and then it comes up again (curtain call). Not all the actors from the play are taking bows(including the actress playing Bob Cratchit's daughter so I felt (even though she was in the climax scene clapping with them) that she too (like the actress as Belle--who was also missing from the actors' bow) was a film projection. (Realize there were projectors years ago that could project an image right on to open air no screen needed.) I think as Magoo was getting ready to go on stage he passed three or was it two actors also walking on to the stage (one of them the guy playing Bob) so therefore they were really there. One of the other men (or just --other man) walking on to stage was a charity guy. There were two charity guys. And both charity guys do not take end bow(just one does)s. So if both charity guy actors were actually in the theater on stage I guess one of them was not taking a bow because they already had too many people in the curtain call as it was. My procedure would also kinda explain how the stage set becomes so artificial in the last moment after it was seemingly so real.