It seems in mentioning other members, the name is not really important, instead it's the member number.
I'll upload a gif since it would be much easier
[mention=41434]zakamanichoo[/mention] the name is actually more important, hence why if the user exists it switches to them, even if you have the other person's numbers (which will be auto-corrected as well).
Also, when I do it I normally just hover over your avatar so I can see your number (via the link), and then type out the mention tags myself. :P
[mention=41434]giga drill breaker[/mention] I think it is probably more lazy this way though. It doesn't take very long to type, and then I don't have to go and edit it, which wastes some time.