How to deauthorize a single computer you don't have anymore, without having to deauthorize all for Apple Books?

How do you deauthorize a single computer you don't have anymore, without having to deauthorize all?

Seems silly to be forced to deauthorize all vs being able to manage them from one's account.

When I get to the account settings in the App Store, it has a separate section for "Computer Authorizations" and another for "Manage Devices." Why are these separate?

The Computer authorizations say I have 5 computers, but there is no way to see a list of those computers. Only the option to deauthorize all.

And the Manage Devices section allows me to see a list of devices, where I can choose to deauthorize certain ones, such as old computers. I went ahead and removed some old computers in this list, so it now says I have only 3 devices, but it appears this doesn't actually deauthorize those computers since it's still reading "5" in the other list.