It appears that this one came into contact with a caustic acid of some sort. Or so my guess. ANACS as the grader, MS60 Details- Damaged
Well I do think it a defective planchette and at the initial strike of the coin it detected from the coin. I say that because of the “N” in one. The edge of the coin where it is missing metal is lower than the fields of the coin and the leg of the “n” is pressed in to the lower area. Which I believe it was striked first and then broke off. I may be completely wrong but from what I’ve been reading on the mint process this can happen..
If the plachet was flawed that would be the weakest point to give way under strike pressure. Which there could or couldn't be retained. So most probably the bank bag of dimes had pieces in the bottom seam of the bag.then again the fragments may of ended up in another bag ,or the floor.