In the 70s, Clare Torry was paid £30 for providing the improvisational vocals in Pink Floyd's "The Great Gig in the Sky" on "The Dark Side of the Moon." Over the next several decades, she received none of the revenue earned from the massive success of this album.

In 2005, she sued Pink Floyd and EMI for songwriting royalties, and reached a settlement with them. She is now credited as a composer of the song in modern releases of the album.

Most session musicians probably aren't so fortunate.

https://en.wikipedia.org/wiki/Clare_Torry