Right but you can sue for what happened on the training server. I'm guessing the training server still exists. I doubt they wiped it completely before the next round of training. If the training server infringes copyright then you still lose the suit. Maybe. Remember that copyright law is not written with the internet in mind. If you have a "copy" and it's not authorized that might just be enough for a backwards court to find infringement.
I think of it in extremes. Imagine you had a video producing model of the future. Could you then load up every MLB game recorded and train the model to make novel baseball games based on that or would the MLB be pissed you had a server full of every MLB game ever recorded?
They have to prove it but if they case gets far enough they will have the right to ask for discovery and they can see for themselves what was included. Thats why it might just settle quietly to avoid discovery.