It might not actually be random. It was stated that Kidd went to WCI to get back something that was stolen from him.
It's possible they had a copy of another Poneglyph, (Not Big Mom's), and it was stolen by the Big Mom Pirates. The Kidd Pirates followed the ship to WCI, and got it back before it could be delivered to Big Mom. The question is, is which one could it be. Doubtful it is Zou's, which means it can only be the one we don't know about yet.