Jeff a,
My best guess is that the dulled bit is from "use ware". The polish on the rest of the ax suggest that the ax was finished at one time, but may have been switched to a secondary use such as pounding Basswood bark to free the fibers after "retteing". There are many outher such functions in a survival culture that would dull the bit like that.
This also may have been a stone that could not "hold" a sharp bit; because it appears to be an overly grainy rock also. They may have just moved it to a secondary use.