Unlike patents, for cooyright, independently created work is not infringing. So, if you build a model that really does actually model music, this could be argued to be independent creation.

But there is also caselaw (involving George Harrison IIRC) on "unconscious copying", where having heard a piece is suggestive that it was not an independent creation, despite not being deliberately copied. So, training on a corpus that includes a specific piece is arguably a case of that.

There"s an interesting question of whether a model is just a sophisticated statistical compression of a corpus, or whether it is a thing in itself. I would say, if it finds patterns that are disproportionately simpler than the corpus, it has found "something".

But another view is of creation as involving a side-channel or one-time pad, in that music is created by a human and heard by a human, who have common information that has never been present in music before (e.g. specific aspects of common neurophysiology, auditory anatomy, exact heartbeat waveform, new sounds/rhythms in the world, new speech patterns, associations between existing melodic fragments and words/emotions/visuals/status etc). In this sense, truly new music is discovery of the Human Music Processing System, which ultimately involves the whole human and their social and physical experience.