They did not need IP law, as to copy anything was extremely expensive and time consuming.
Do you have any idea how long it takes to typeset a book by hand? Or to paint a reproduction of a picture? Or to get an orchestra together to learn and play a piece of music?
You could not just anonymously get a copy off the pirate bay.
There were less people doing it too. It would be bloody obvious who made the copy, and who made the original. I bet you that people had their own, perhaps violent, ways of resolving these issues even if it was not coded into the law.
The situation nowadays is completely different. The way artists and audiences interact is by mass distribution of recorded media, which is impractical without IP laws.