You're not wrong, I believe Brian Dickmentioned this point as well in a previous post!
It occurs to me that the other likely outcome of cocking piece impact onto the rear of the bolt would be sheared firing pins somewhere near the thread origins. Oddly, I've none in the "dead parts " stash!
ETA2:So the burnished or shiney face surrounding the firing pin hole of the cocking piece below is likely significant!
ETA1: Whilst posting, here's some supplemental photos to subjects previously introduced:
The uncleaned cocking piece showing the multiple roughly parallel (or slighly convergent?) fracture planes that are linked by a longitudinal fracture. Ref. Post #21
Early Glock G17 w/ crack in ejection port through a portion of the proof mark. Note the newer slide above w/ the proof relocated...Ref. Post #36