Probably not much. My uncle was an attorney for many of the phantom labels in the Sam Phillips' recording world in Memphis. Dear old Uncle was a sheister's sheister, yet even he was embarrassed at how the artists were sucked dry by layers and layers of production and management fees.
I have always read similar, and the key to money is songwriting royalties. This is why old stars keep touring until they should be retired: they make money performing live, not from old recordings, I gather.