How many authorizations do I really have? And how do I deauthorize all?

I have a newish Mac Mini. I went to play a purchased song in Music, and I was told I had to authorize the computer. So I signed in, and was told that I have authorized 5 out of 5 computers.

I was curious to know what other computers were authorized (though I now know that it'll only show you the number of authorizations but not what the devices are) so I went to Account > Account Settings and it says only one machine is authorized. Further, unlike in the screenshot here, there is no Deauthorize All button next to Computer Authorizations.