Newer players have missed out on the chance to get old cosmetic pets and may find it difficult to catch up.
In the past, the devs have helped this issue by having a cosmetic pet day on Saturday on occasion. One of the biggest issues with them is that they block other pets for the entire day.
What I propose is that 1 in 4 vault weekends use a separate drop table of pets with cosmetic pets instead of non-cosmetic pets. This would provide new players with an opportunity to catch up on missing pets plus not block further pet rescues.