The typical Chinese pantang of do not celebrate AFTER the actual day, is to avoid the "celebration is in the past".

Another old saying is, the actual day is already added one year, if celebrate again later date, which means adding an extra age to the host 🤣 wonder why Chinese tradition add 3 years on the last day?

Sorry to bring this up, I know it's ridiculous but fun to talk about. FYI only. Since we're still early, wish your dad a very blessed birthday and fruitful years to come. Cheers buddy.