It is not necessary for the blue-eyed people to know the total number of blue-eyed people in the tribe, they can deduce it at day 100:

  * A blue-eyed person observes 99 blue-eyed people.
  * On day 99, the blue-eyed people do not commit ritual
    suicide.
  * Thus each blue-eyed person learns that all the blue-eyed
    people also observe 99 blue-eyed people.
  * Thus the blue-eyed person knows that the other blue-eyed
    people must observe that he/she has blue eyes.