There's only about six million active containers in the world. If one owner has more than a sixth of them, an easy fix would be to issue them a second owner code, basically extending the six-digit field by a bit.
This was their source. Apparently not updated since that 2012 survey: https://www.csiu.co/resources-and-links/world-container-flee...
Huh, that's a lot less than I expected there to be.
I would guess that the next answer is "Evergreen gets multiple Owner codes", because that's a real simple way to stretch it, but...