That’s why he rips it up so he can have the only three left
"No really kaiba, you can only have three at a time. Its in the rules."
@Hatori, "I'm not going to let a technicality stop me!" - actual 4Kids dialogue
@Hatori, 3 at a time in the deck. Technically you can own as many as you want as long as you don’t try and play 4 of them.
But he has to make sure the BEWD is never used against him, so screw grandpa.