Celebrate pet birthdays?

Since all three of my dogs are rescues, we have no clue what their real birthdays are. Instead, we celebrate their "birthdays" on the day we got them! We don't do much, but us humans eat cupcakes because let's face it - any excuse to eat cupcakes is a good one! We give the dogs extra treats (but fair, equal amounts between all three of them, hehe) and sing Happy Birthday, but it ends up being mostly for our benefit. They probably don't even notice anything is different!