Tumblr Follower Technical Problems

Help! Does anyone know why this would be happening? A few times now I’ve gotten a new tumblr follower and yet my number hasn’t gone up. So I counted (I don’t have that many followers and yes I was determined to get to the bottom of this) the list of followers to see if it was correct…. and its way off! It’s like 20 short of the number which is a few short of what if should be because it hasn’t been going up when people have added me… I don’t know why this would be happening. Does the follower list not show all your followers? I counted twice guys… I’m so confused and I can’t find the answer anywhere.