Why would a library have records of who borrowed what? The old manual system in the UK worked on a system where your library card was a sort of envelope into w

Why would a library have records of who borrowed what? The old manual system in the UK worked on a system where your library card was a sort of envelope into which the book's card was placed and then it was placed in a tray in chronological order. When you returned the book you got your card back and there was no trace. The library would only be able to say who had the book at the moment when they were asked not for times in the past. See https://www.1900s.org.uk/1940s50s-library-systems.htm https://www.1900s.org.uk/1940s50s-library-systems.htm