Since your daughter will not know the difference, are you worried about what other people will think? As long as you celebrate it some time, don't worry about what other people think. The point is to celebrate your child's first year of life.
Learning to be flexible will teach your children to also be flexible. What happens if one child's 16th birthday falls on another's day of graduation, for example? If your children learn that a calendar does not dictate their life, then they will be happy to go to the graduation and plan a birthday party on another day.
I have a sister-in-law that skipped her sister-in-law's wedding because she had the nerve to have the wedding on her 21st birthday when she wanted to go to Vegas... (Obviously, I am being sarcastic.) We can all guess how the first sister-in-law was raised.