THE HIT MAN: If a tournament is set at say 1500BKR and below to sign up, a player can only sign up who is 1500 and below. However if that tournament starts weeks later, and that player has moved to 2000, they will still be included. It's up to the creator of the tournament to remove anyone from the tournament before it starts if they are over 1500.

In addition, if you let unrated players sign up, after 4 completed games they may also be over 1500 BKR.

I think that explains it.