It all depends on exactly what they sold and what went into the contract.

In theory they could sell any combination of rights. They might be selling the entire catalog and all the rights that come with it, or it might just be a subset. For example, "You can play and sell any of my songs you like, but I reserve the right to perform any of them live whenever I want." Or "You have full rights to everything I've written up to now, but no claim at all on anything I do in the future."

Like any contract, it's almost infinitely negotiable.