Not sure what site you're referring to but yeah, they aren't canon. However, I can see those working as well!

But that's the problem with having to pick birthdates for characters that don't have one stated in canon: not everyone will agree on the same one. I know my least favorite part about writing Z apps (besides writing apps period) is having to pick a birthdate, because I am afraid about picking something that people might think is "wrong".

Eh, but if it's something that I think still fits, then whatever. It seems like the main thing the birthdates and zodiac signs are used for anyway are for housing districts and when a character gets their birthday card.