Sometimes the camera zooms to another part in the same tunnel, that's why the ammount doesn't change for that tunnel.
Every time you save a Mud, the ammount displayed decreases, so when you leave an area the number showed should be 0 for that tunnel.
When there is no tally board on the beginning or the end off the tunnel, you can always check your status by going to the pause-menu (only in AE that is).
I hope it helped!
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