When you know you know a lot of songs

So we were watching an episode of the Danny Thomas show from 1956. The beginning was not the chorus, even, but I said, "This is going to be 'So Long, Oo-Long (How Long You Gonna Be Gone?)'" and sang the chorus, but I wasn't believed. Sure enough, that's what it turned out to be. Harry Ruby (of the song-writing team of Kalmar and Ruby), of all people, was on the show. What I didn't realize is how old this song is: it dates from 1920. Everybody sang, and most played the piano, and well. They all had an encyclopedic knowledge of songs of all sorts, from hymns to folk to Broadway to art songs and opera. Some of that has lodged there in my brain for decades, and useless details float up to the surface at unexpected times.