This reminds me of a game. I was at the Banff Centre once, taking in a master-class given by Oscar Ghiglia. There were perhaps twenty guitarists in the class. Several of us were hanging out in a dorm room one evening and there was one guitar there. Of course, everyone wanted to play the guitar. The game was: whoever had the guitar had to play the first four bars of whatever piece someone named. If they could, they kept the guitar for a few minutes. If they couldn't, they had to give the guitar to whoever had named the piece. "Ponce, Prelude 7". "Castelnuovo-Tedesco, Sonata, minuet". And so on. One guy was almost impossible to stump. He knew virtually the whole repertoire. I think he is guitar professor at Cornell these days.
I was able to demonstrate an interesting kind of expertise once. A friend of mine, the fine Beethoven scholar Bill Kinderman, who had just published a study of Beethoven with Oxford University Press, had given me a copy. Somewhere, if I recall correctly, he quotes, without attribution, the German philosopher Ludwig Wittgenstein saying something like philosophy is like a ladder you use to climb up onto the roof. Once you are there, you no longer need the ladder. I had actually read some Wittgenstein so the next time I saw Bill I mentioned that I recognized the quote. He looked at me with some surprise and ever after did not regard me as just another performing musician.
Knowing stuff is cool. Another quote from him concerns music (Ludwig Wittgenstein's older brother Paul was a famous concert pianist):
It is so characteristic, that just when the mechanics of reproduction are so vastly improved, there are fewer and fewer people who know how the music should be played.