I saw 3 usernames on NameMC that have periods in their names. They are all unmigrated but people still use them becuase the first time i looked at one of them they had an earth skin but now they have a regular person skin.
Usernames:
https://namemc.com/name/.Flow
https://namemc.com/name/Mr.LoL
https://namemc.com/name/internet.com
The uuid is in the mojang system.
https://api.mojang.com/users/profiles/minecraft/.Flow
https://api.mojang.com/users/profiles/minecraft/Mr.LoL
https://api.mojang.com/users/profiles/minecraft/internet.com
I think the people who made the names made them when name restrictions were not done yet.
Linked issues
relates to 1
Comments 3
Apparently intended, see WEB-122.
That's probably it (similarly there's accounts with 1- and 2-character names from that period).
For reference (though this turned out to not be useful), here's the name history results (which don't include the time of creation, unfortunately): .Flow, Mr.LoL, internet.com.