I’m pretty sure 8.0.100.1 isn’t incompatible with newer versions, so even if someone installed it they’d be able to do Send/Receive and otherwise interact with the rest of the team.
I suspect what you remember about 8.0.100.4 is actually with the updating system. There was some change that happened early on in the update process, where they switched where the system looked for updates. As a result if you update within PT, you’ll first download the update for 8.0.100.4 (which was the last update at the old address) and then after installing that you can download newer updates. It actually may require a second set of updates… I don’t remember.
To avoid that I usually download the newest update and install it directly right after installing the base version.