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The Shop and Heiser ran out of brown button logo snaps twice during their tenure. The first was very early 50's. The second was very early 60's. This second time was for a much shorter period of time and only a limited number of models were affected. Here are a couple of examples of 3-6 sheaths from that period:
There are a couple of disconnects between your first sheath and these early 60's sheaths:
1. The snaps are different. I've seen your snaps on early 50's Heiser sheaths and "Johnson Casselberry" sheaths, but not early 60's Heisers. Your diagonal keeper rules out early 50's.
2. If the sheath is original to the knife, then the early 60's are ruled out because for all intents and purposes "pinning" a stag handle was discontinued after 1957.
Bottom line is I don't have an explanation for those snaps.
Some Heiser sheaths from the early 50's exhibit that "II" mark as well as model or blade length numbers. To my knowledge, no one knows why, but it was a fairly common marking. Some have hypothesized that the marking designated a specific Randall dealer.
Sorry I couldn't be of more help. Maybe someone else can shed some more light.