I'd love to use some cool 1929 music for my project, but it's difficult to find recordings and even more difficult to determine whether they are available to use. For instance I'd love to use Bolero and there are several recordings on Wikimedia Commons, but they're post-1929 recordings and I'm unclear on why Wikimedia is categorizing them as public domain.

Musopen has wonderful Creative Commons modern recordings of classics, but their selection is very small: https://musopen.org/

Where are you guys getting your music?

Note, *recordings* are only in the public domain if they are from 1924 and earlier. If you want to use recordings, they must be recorded 1924 and earlier. Even if the music itself is in the Public Domain, *recordings* aren't unless it is recorded before 1925. If you are looking for recordings, try archive.org.

Bolero is in the public domain in Europe. Specific recordings are covered by a different law, as noted. It's possible the recordings are PD in Europe because of Life+70 laws. (Plus weird extensions. The owners/former owners of Bolero are fighting like the Doyle estate to keep it in their hands as long as possible.)

https://www.reddit.com/r/copyrightlaw/comments/mysehl/why_is_bolero_by_ravel_not...
https://www.techdirt.com/2016/05/04/copyright-holders-try-to-stop-ravels-bolero-...
Bolero was first recorded in 1928; it'll be a few years before that recording is public domain in the US.