Small note, idk if it's intentional, but right now the calculator shows 32 pets for July 2008, and 67 pets for Christmas 2008.
However, one of the pets in there, the brown hooded rat, is actually a
double release. The same rat was released on two separate occasions, and it functions as one and the same pet in the archive. (You get checkmarked inboth archive tabs at once!)
So the number of 2008 pets should actually be one less than is currently shown.
Furthermore, the special releases tab in the archive for 2008 also includes the Tess birthday litter, which is the equivalent of a release that would be sorted into "Staff birthdays" in later years. Unlike the "Unreleased" pets in the same tab (which came from the December 18th box), the birthday litter was a regular 'holiday' type adopt and you could adopt each giftbox individually.
There was no RNG involved in receiving these pets (unlike the luck of pulling a UR pet from the 18th), so I'd argue that they ought to be included in the total count for 2008, and not excluded from the year count / treated as a special release.
I understand if that's what you prefer for the sheet since the archive
does put them in that tab, but purely in terms of obtaining them, they were really not different from stuff like Valentine's day or other birthday pets.
The total number of pets for 2008 is 211.
(207 if you exclude the UR pets, and 201 if you also exclude the cake litter after all.)