New Gamertags

I've been recently considering changing my name due to people i have had falling outs with having similar names more specifically 3 of them have an xz at the beginning of their name as do i but as i've gone to change it i've noticed now its always trying
to put the suffix in my name when using the new characters, i've tried looking up the tags im trying to use but according to the search they don't exist but something i've noticed is that even when using the new characters it corrects it to a letter for instance
i was trying λtlas which is a usable character but i've looked for that gamertag and no one has it so is my gamertag getting a suffix simply because im using the special character? And then it says in games
that don't support it it will appear as Atlas0000 random suffix, so is it cause the correction its making for games that don't support it is taken? Im a little confused about it all any help will be appreciated thanks i wont change it till i know

:)