Permission Sets and Permission Set Groups: Shared values and silly rules
So, in experimenting with converting existing batches of Permission Sets into Permission Set Groups to ease the eyesore of having 100+ permission sets per user, I found the following interaction: Permission Sets and Permission Set Groups occupy the same developer space and as such, share unique developerNames. Nope, no 'Tier 1 Access' Permission Set and 'Tier 1 Access' permission set group.
In fact, Permission Set Groups are basically just a concatenated string of existing Permission Set Id's. They do not carry an actual recordId (if you export Permission Sets, the Permission Set Groups also get pulled in despite it being a 'separate' object; the recordId for Permission Set Groups just link you to the setup page for the Group; Permission Set Groups share the namespace prefix among Permission Sets as well.