Notes For getting books from other libraries:
Copyright is unheard of. If you own a copy, you can make new copies and do whatever you want.
Books are leased commonly, and then always under cow and calf.
Library hospitality is common.
Books are commonly traded in kind - that's a win-win - both libraries increase their power.
Books are gifted and traded for political favour when appropriate.
Books copied and sold for vis are almost never the best books around; selling copies of the best books reduces the (relative) power of a library. Weak libraries have little to lose and are likely to sell copies, but they do not have the best books.
Many of the books sold are inferior copies, possibly copied many times, loosing a few random sentences or paragraphs each time. E.g. the root you can buy was probably a sound L8Q22 summa as authored, but after ten generations of copying and some pages lost on the way, it has ended up as L7Q17 which is vain in [Cov] jargon. Maybe you have the root, but one day you discover a better copy worth buying.
It is almost impossible to get a complete overview of available books on the market. The redcaps have good records, but they use their knowledge to make a profit.
None of the rules above are universal, or maybe 8 is. Exeptions and variations make the norm.
I think these principles make a more medieval feel, and we avoid anachronistic interpretations of copyright and calves. To make it work, I need to contradict RAW on one point. The book prices in [Cov] must be changed to leasing, possibly long-term, like 70 years, simply to fit with a historic version of Cow and Calf. What [Cov] has down as vain books can be sold though.