Connie's wedding gave us a great introduction to FFC's fanatical attention to detail, and the old guy provides a sterling example. If you look very closely, he's got his glasses in the breast pocket of his coat while singing. A very realistic touch: vanity would prompt him to take off his glasses for his show, but he'd put them in an accessible place so he wouldn't forget to don them after he got off the stage.
Other nice touches in that scene:
--Any movie set in the early Forties will show men wearing short ties (saved silk for parachutes during WWII). FFC showed the young girls' hair tied with wool ribbons--another realistic touch because silk and rayon were needed for the war effort.
--Any producer or designer can rent Thirties and Forties cars. FFC made sure that they had gas rationing stickers in their windshield ("A" visible in lower corner).