Remember we need to talk about law as it existed back when this happened not the law today. Back then you didn't get copyright protection unless you registered with the copyright office (and a few other things that I'm not quite sure of - none relevant to the law today). So the copyright was never registered, likely because the distributor was expected to register it and they failed to do their job. There might be a lawsuit against the distributor for breach of contract, but it wouldn't be a copyright lawsuit.

Today things are much easier, if you create something it is copyright. If you want to sue you need to register, but you can register at anytime. If you register you can sue for triple damages for anything that happens after you register, but you can still get damages for things that happened before your register. (The above is my understanding of the law, but I'm not a lawyer)