Perhaps as many as 72 of them? :) What I'd love to know is how the Bible would have read, according to Apostolics, if she HAD said "no". Would God have admitted man's power over Him, or would the whole event never have been reported? Have there been thousands of other examples where man said "no" to God, thus forcing God to change His original plan, etc.? Perhaps the way history has unfolded is God's 10 billionth best plan, as deviated by man. It must be by shear luck that we are even still here. :)
This is not biblical or church teachings, but I would suppose that if Mary had said ‘no’, then she may not have included in Scripture.
We don’t know; all we know is that she said ‘yes’ and we are where we are because of that acceptance.