one thing about four score is you can take a picture and it scans.  basically most of the sheet music now is archives of how a class or lesson went.  and if theres any type of "concert" its good to have the order and music right in front so everyone is on the same page.   for those ocasions i keep to printed music in the plastic sleeves in a small 3 ring binder.   

i can organise within four score by tune type.. e.g jig reel waltz..etc.   so handy that way.   also can backup and keep the archive on a local computer.  or on the ipad.. or on the cloud.

i dont know how many tunes i know.  only a handful maybe. probably somewhere in the 25-50 range but thats ones that i think i could start and finish without having to rely on someone else playing before i was able to play without any sheet music.  

no