Myself as well as a lot of other people handle brass a lot from picking the brass up all the way to loading. I usually find cracked brass before seating the bullet, however I have caught them during bullet seating. When seating the bullet on my LCT I have felt an initial tightness then the ram just basically goes limp,(something I like about the LCT I can feel each process and stop immediately if something doesn't feel right) then I check it and sure enough it is cracked. If you have a progressive press you may not noticed a crack when seating the bullets. I have had/heard them crack when sizing. I have even I will tell you though I did catch a cracked case once when loading a magazine. More importantly you caught it.