This rule may though mark groupings as erroneous, which are perfectly valid in large parts of the world. E.g. the https://en.wikipedia.org/wiki/Indian_numbering_system[indian numbering system] uses groups of 2 and 3 digits (as famously explained on https://www.youtube.com/watch?v=l4bmZ1gRqCc&t=275[Numberphile]).
Were such systems left out intentionally, or just not thought of on rule definition?
Even though i'm not really affected by this, i felt obligated to bring this up.