Clones came out in September, This rule was printed in December. I don't remember honestly when they changed/added the rules
I'm just saying part of creating/selling the game is making the easily accessible and fore-seeing these kind of issues.
You may not think its an issue. I play very casually with several other players, some of whom are under 18 with limited access to the internet. Releasing Core rules inherent to playing the game in such a way is sloppy. I've played with and against clones since they were released, I am on this website several times a week and had honestly never seen or heard of this rule