Comment by thinkingemote

Its legally required, but in practice a large amount of publishers do not submit a copy, and there are no real consequences for not following the law.

This illegal non compliance becomes much more common in expensive books, digital-only publishers and in data publications which are commercial.

E.g. think of some very expensive report on data centres aimed at the hedge fund trading market, government procurement datasets, geodemographic data, credit risk databases, bloomburg trading data etc.

If it's published, even if it costs a lot, it should all be viewable for free in the library.