Hi, Claire - you're pretty safe with songs published before 1923, with a few exceptions. Performers and arrangers can claim copyright on post-1923 recordings and arrangements of earlier songs. When we did the Rise Again songbook, we had to pay rights for Carter Family songs, even if they were written by somebody else before 1923.

If a venue owner has received a threatening letter from ASCAP, he/she would be unlikely to want to bother with the hassle of fighting ASCAP. So, another venue bites the dust or pays the fee. There ought to be a better way.

-Joe-