> Or are they just using it for training

You’re making a distinction here, but training is something you repeat for every new point release, so you need to keep the data if you want to use it for training.

They are. They can’t release it; that would be copyright infringement. But they’re absolutely planning to make further use of the book later.

The data of such a copy is nothing compared to the wider picture and the data can be used for future training, so even from a purely self interest perspective, they should be keeping the copy.

As for long term benefits, it could one day be sold as a service, once copyrights have expired on the works. We can't see it today, but that is purely the result of the law and what the law intended to do from the start, you don't see a copy unless you pay for your own.