I don't mean newer pets getting their rarities assigned on the 15th, obviously that happens. I mean older pets that already have values attached. I know that rarities are determined based on pet quantity in circulation, not pet holdings, and that it's percentage-based rather than flat values- if one person has all the Smiling Panda Hat Cats, but they have enough of them to give one to every player on the site, it's still going to be a 0-star. But in a year or two, enough players might have registered that there aren't enough Smiling Panda Hat Cats for everyone to have one anymore. More of a 1-star situation.
Will pets gain stars over time as more players join and their relative rarity goes up? I assume that's how all those old pets got to be so rare, and the early days of the site weren't just Rainbow Rares For Days, but I don't think I've ever seen it happen myself. Does it happen? How common is it? Is it automatic on the 15th, or is it more of a once-a-year thing? Do rarities ever go down post-12/18? No one ever talks about this, so it doesn't seem to be a significant component of the economy, but I also don't see how it can not be. Aren't there people holding onto their 4.5s awaiting the day they become full 5s and appreciate in economic/sentimental/coolfactor value?
Really, I just want to know if/when I should be checking my trade folders for guys who are no longer accurately sorted, and whether I should be going through every page or just checking the last page with the oldest guys.