Oh, I know that CS fuzes were less then reliable. Or, maybe better, less than consistant. Especially when comparing arsenel to arsenel. I've read that that was one of the big causes of the overshooting at Gettysburg - the fuzes were from a different source, so the gunners and cannoneers were not used to them. It wouldn't take much difference in burn rate to cause a 100 yard difference in point of detonation. Heck, it could even have been a slight difference in the cut marks on them and not the burn rate.