^ I don't consider pets below C to have any value either tbh, I mostly use mine for gifts if I have any on peoples' wishlists. But newer players are unlikely to have pets above UC to start off with, so I included the lowest rarities since they would likely make up the majority of a newer player's trading stock. Giving them more tangible values could help a new player work their way up to higher rarity pets, even if their goal rarities are UC/VUC.
I'm not sure if we should be trading 1C for 2C for the case of a large date range, if we are also going to say 1UC = 2C. Because that essentially creates a scenario where 1C = 1UC with a date gap. I would never trade an UC for a C though, regardless of date. I can't
In the days of olde, date ranges were vital because the rarities were inaccurate as many old pets were trapped on inactive accounts. So an older UC was way rarer than a newer UC in terms of trade availability. Once old inactive accounts were excluded from the count, the older pets mostly moved upwards in rarity, so you were comparing a rare to an UC which is how it should have been.
Now that we have this new rarity update which brings a much higher granularity, I am not convinced that we will have many scenarios at all in which an old pet of a lower rarity should be worth the same as a new pet of a higher rarity, excluding VRs+. A 2012 common is less rare than a 2023 uncommon, so it should be worth a lower amount despite the date surely.
So if we have a 2:1 ratio between rarities, then the age gap should be closed at a lower ratio, is my proposal. So this means for a 2012 common, a 2023 common should add a (preferably old) VC. If the 2023 common has to add a second common, then this same pair of C pets would technically be the same value as a 2023 UC. This all assumes a 2:1 ratio for trading between lower rarity pets though. If the community decides a 3:1 ratio is better instead, then this would no longer be an issue (because 1UC = 3C, so it's fine for 1C = 2C that are newer since it would not bump the value up into the UC range).