No. It would only create more confusion to the topic of Kopa when it comes to fanfiction vs. official. To deliberately create some commonly "celebreated" birth date while many people are too lazy to check if it's for real or not and then there would eventually be yet another fanfiction vision paraded as official. And it's frustrating enough already as it is.

Better off just everyone keep making his birthday to be whatever one individually prefers.

If you really want to do this, I'd suggest you to contact Alex Simmons - as in the guy who created Kopa - and ask him to decide a birth date for Kopa. Instead of making a big number about some fan-made date.