The modern concept of "intellectual ownership" didn't exist back then, I think. Composers were borrowing from each other all over the place. Handel was a particular culprit; often he transformed his models into something quite different, but also often he just left them as they were. If Vivaldi had known about Bach's strange arrangement of his piece, which I'm pretty sure he couldn't have done, he probably wouldn't have minded particularly: his op.3 collection, containing that four-violin concerto (and two other four-violin concertos too, among other things), had been published and I'd presume he'd been paid, so the music was in the public domain and people were just as welcome to arrange it for different instruments as they were to play it.

I thought Ravel always got his credit for Pictures, especially as he wasn't the only one to arrange it for orchestra.

Do tell more, autoharp . I didn't know that. Ambiguous references to unspecified 'assisting' in the programme by Ben Mason(?) and Malcolm Bennett(?). Goodness, John Harle and Jane Manning no less among the performers. I don't remember that registering before.