Originally Posted by hayabusa8

[A] = 1 chance on 26 that a clan choose the tag.
[Au] = 1 chance on 52
[Aurora] got 6 letters =(6 x 26= 156) 1 chance on 156 that a clan choose this tag. [Maybe it's more than 156]

Mathematically, more the tag got letters, more the probability to have 2 same clan-tag is high.