a little late to put my opinion in but where you guys were saying that thousands of a pet would need to be deleted? I dunno this is how I would imagine it being..
(making the numbers small to make it easier to explain, not real numbers)
Say there were 2000 of a certain spider on the site. The rarity was very common. But it was at the very low end of very common, lets say... the largest amount of pets befor becoming omg so common would be 4000 of the pet.
In the database, to make a pet go from very common to common, you would need 1900 or less.
If you deleted 200 pets, it might not seem like it would make a big difference, but it pushed it under that 1900 mark, thus changing the rarity.
If that theory is correct, couldn't deleting 50 spiders possibly change the rarity?
unless rarities work differently and im just rambling :P I apologize if this doesnt make sense xD