We reprint old books after checking out copyrights (for all books, this means pre-1930, but for some (I'd actually say most) it also means ones published up to 1964 and 1973, depending on how the rightsholders did (or didn't) do the renewals). We use a special guillotine type cutter to cut off the binding and then store the pages in a sealed plastic bag which goes in the archives; they're stored there indefinitely in…
The value of most very old books for AI training is very low. You don’t really want your AI training data to start biasing toward outdated writing styles. Most of the valuable knowledge has been covered again in modern texts in more depth and detail.
There is interesting value in old texts and it’s important to have them archived. It’s less valuable for stirring into the giant pot of AI training data, though.