I say it about birthdays and holidays. You can celebrate your birthday any day you want but your birthday is your birthday. It is not a variable feast. Ditto any celebratory DAY. Sri Lanka Independence DAY is February 4. You can celebrate Sri Lanka Independence on the 3rd, 5th, 6th, 7th or 28th. But Independence Day is February 4th.
Maybe Google, being California-based, will do a Google Doodle for the 6th rather than the 4th.