That is curious. It is entirely possible that the same person did the initial ordering for both libraries.
From what I understand, and I am not an expert in it, there are standard book lists and also standard packages that you can buy from book vendors to equip a new library. So you look up "Public library" and the American Library Association says these are a good starter kit, and you contact your state library association and they recommend an additional starter kit. And you also load up on subjects of regional and local interest.
For academic libraries, you start with the academic starter kit, add in packages for the different course areas that your university teaches, and also look at the state board for local recommendations.
I'm sure there are plenty of libraries who do their initial kitting-out based on sheer whimsy and looking at other area libraries.
no subject
From what I understand, and I am not an expert in it, there are standard book lists and also standard packages that you can buy from book vendors to equip a new library. So you look up "Public library" and the American Library Association says these are a good starter kit, and you contact your state library association and they recommend an additional starter kit. And you also load up on subjects of regional and local interest.
For academic libraries, you start with the academic starter kit, add in packages for the different course areas that your university teaches, and also look at the state board for local recommendations.
I'm sure there are plenty of libraries who do their initial kitting-out based on sheer whimsy and looking at other area libraries.
How they do it in the UK, no clue.