Copyright issues in the music industry are a minefield. Particularly when artists change labels.
In the Everly Brothers documentary, Don Everly said they changed record labels for a lot of money, going from Cadence to Warner Bros.
This meant they couldn't record any more F & B Bryant songs who wrote nearly all of their hits, nor anything they wrote themselves as Cadence who owned the rights to the music, wouldn't allow it.
They wouldn't have been able to make a compilation album which contained hits from both labels.