I believe that if Mistral is serious about advancing in open source, they should consider sharing the corpus used for training their models, at least the base models pretraining data.
Maybe they could share a list of the content of their corpus. But that wouldn't be too helpful and makes it much easier for all affected parties to sue them for using their content in model training.
That would almost be worse. All copyright holders would need to do is search a list of titles if I'm understanding your proposal correctly.
The idea is not to get sued.