The 68 reporting to roll call is an arbitrary number. In the chaos of that day and the days following, they don't know exactly how many showed up to roll call. The 68 is likely taken from a roll call in one location while other soldiers were in other areas. My grandfather was retrieving men (alive and dead) from no man's land that night and wasn't part of the roll call but he survived the battle. In my research, the belief is that more than 150 would have responded to roll call had they been intact.