Nitpicky stuff:
Second post:
first quote
"Like Ice Rat" -> "Lime Ice Rat"
Drink Me didn't turn in Jan 2019 although it was close, so maybe change the wording at the top to "The pets listed on red are significantly out of place following their rarity increase to omg so rare from very rare during the rarity overhaul in early 2019
or shortly afterward".
second quote
"Two omg so rare UR pets," you should put a line break before this
third quote
"two tiers above
most of the other advent dogs in their litter"
"sit with the rest of their litter-mates on tier 7
since they're all about equally rare"
last quote before the old list of to-be-discussed pets
"Throughout the years of the list, new UR pets were placed on the main list about 1 year following their release
on December 2018 during the advent calendar."
"These pets went up in rarity at the same time as let’s that were on the list" let's or pets

I honestly have no idea about the dragons don't look at me LOL I could try digging around, maybe, if you want me to, but those links looks good
edit: I remember reading something earlier about which dragons were in which litters/released which way? Was it this thread or a different thread? The one thing I can tell you is that the copper, green, and gray malk dragons were in the same litter as shown in the archives, and the others had special releases of some kind (white released like zebras but with malks, not sure about red or blue)
edit2: it was another thread