I think there are probably more actual White Walkers. Most likely almost a hundred based on what we know.
I disagree, it seems there might be 13.
Minus the 3 Jon, Sam and Meera killed and plus that baby white walker, assuming a baby white walker grows into a full on BD white walker soon after that ritual.
Which actually brings me to a thought I had rewatching The Door again yesterday, Meera killed a white walker with the same kind of spear the child of forest tried to kill him with a moment before and fails, thoughts:
- It's odd that the child of forest didn't know normal weapons are ineffective against the white walker as she tried to stab him with the spear, highly unlikely.
- They could have had just the one dragon glass/Valyrian steel spear in the cave, also highly unlikely IMO, especially when it wasn't kept anywhere special, Meera just grabbed it off the floor.
- It's revealed that the white walkers were made of dragon glass and it's probably why it kills them, why was Jon able to kill one with Valyrian steel? We're assuming because it comes from the same place dragons came from and because we actually saw Jon kill one with Longclaw.
So my crazy thought is that Jon Snow didn't manage to kill that white walker in Hardhome because Longclaw is Valyrian steel, but because of who Jon Snow is and the same goes for Meera who killed the white walker with a mere spear.
The weakness in this theory is that Jon did grab a different sword in Hardhome and attempted to attack the white walker with it but it shattered upon contact with the walker's weapon, which if my theory was true would mean that Valyrian steel could withstand a hit from the walker's weapon but it won't kill the walker himself unless it was yielded by Jon Snow or Meera and that's a bit of a far shot.