By comparison, I have looked at CNo.7 .22 rifle chests and found there are clear variations. All are genuine. One researcher will look at the piece in front of them, and state X as a fact. Well, for that one piece it is a fact, but not for the others not available to consider. For example, Canadian made CNo.7 chests have slotted screws and combination Robertson and slotted screws. The combinations are a dead giveaway it was made in Canada (God bless you Mr. Robinson), but the presence of slotted heads suggests the manufacturer worked closer to the written specification. Perhaps he expended all slotted screw supplies before requesting permission to use combination head screws. Drawings get changed for all kinds of reasons, and sometimes a particular method/tool/resource is not as abundant in one circumstance as whoever made drawings anticipated.