yep.. that does look like a flaw/fissure and not a regular mouth crack.
ditto what i'm seein on the laod in a few books too. a lil light.
seeings as how it's doing it to more than 1 case..
i'd check the entire lot with a lstrong light and even look inside the mouth at an angle.
you sure this was new in new un opened packaging?
I've bought win brass marked new at a show one time.. in a win bag. got home and bag had been slit and taped and the brass in it was at least 1x fired. it WAS deprimed and tumbled.. I DOD find tumble media in it!!! and the COL was out of spec on some... i know they don;t send you pre-grown win brass.