30-32 seems to be all from the website. I guess after hundreds/thousands/millions (the number that SPG probably wants to be corporate property) they move on to the next number. So xx30xxxxx ended in 2003 (from what I read), xx31xxxxx ended in 2007.

At work we labeled samples for external testing and just changed the order and added a random number, I didn't choose this numbering and it was very easy to understand what each number meant, but then I wasn't the boss, so who cares . (actually I did care, but didn't want the potential conflict)