Thanks guys.
It’s certainly a complicated little device.
I thought the button was for unmounting.
I pressed it and now I can turn the other ear, which in turn makes it so the aperture simulator has proper travel.
I looked online for some photos of it, and it’s an extra hole or at least one for sale on ebay doesn't have the hole.
I took it out into the sun with a magnifier and noticed the hole has no threads so a screw couldn't even be mounted.
So I’m just going to go with it was mistakenly drilled at the factory, or it’s an assembly/disassembly pin hole removed in later revisions.
note: No 4th hole.