I took 15 years or so off from playing guitar and singing, in order to play mandolin and then fiddle in tune sessions around Manchester UK. I learned loads of tunes by ear. I also learned to read music and learned loads of tunes from books. Allen's was the first and O'Neils next. Donal O'Sullivan wrote a well referenced life of Carolan which included all the tunes he composed and other tunes attributed to him. I first got this from a library and was later able to buy it online.

Now there are loads and loads of tunes available on line. The Session.org has a tunes section in ABC which can display the tunes in notation. If I have this right, Jack Campin has a web site with a large ABC collection of tunes freely available.

I suspect that lots of players at Steve Shaw's sessions also learned from books and from online. And from vinyl, mp3s and CDs too. Anyone who only learns to play by ear today leaves themselves open to accusations of laziness.