Agreed ;-; about doubling up birthdays. They could make a more humble/shy or something personality that makes villagers not want to celebrate their birthdays, rather to celebrate others. kind of sad but it works xD or take out the least favourites to make room for the old or new.
Why can't birthdays be on the same day? That would be very simple to add. Also what happens currently if your birthday is the same day as a villager in town?