Very interesting observation Tom. That 3 definitely displays a bit more rounded shape. Definitely not flat, but not high rounded like the new style displays. Notice that it also displays the serif like the old style serif number stamps do.
The new style number stamp seen on RMK east facing Johnson baby dot sheaths are plain without the serif. With the exception of the number 1 new style number stamp. It displays a straight out to the left serif, whereas the Heiser stamped, and West and Horizontal RMK stamped sheaths, on the number 1 stamp, display an angled down serif on the left top of the number.
Great find, so now we have found a slightly different old style number font shape associated with a Heiser stamp.
Thanks Tom

samg -for my personal understanding; can you put forth your hypothesis with regards to numeral style stamps?

Your hypothesis is imperative, lest we all chase stamp styles down a rabbit hole. Thank you.

Sam, also notice the 6. It looks identical to the new style 6.

My hypothesis is, with all the photo evidence that I have observed, is that in the period from approx 1960-1982,(I used the date 1982 because on page 154 Pete Hamilton lists Maurice Johnson as RMK sheath maker to that year, and extending that date range gives ample examples, though my focus is primary 1960-1964 or so) to include brown button and baby dot sheaths, my hypothysis, or theory is that:

1) West and Horizontal RMK stamped sheaths exhibit the old style serif number fonts as seen on Heiser stamped sheaths.

2) East facing RMK stamped sheaths exhibit the new style font number stamp found on all Johnson baby dot sheaths.

3) RMK stamped sheaths without number stamps are East facing.

I am not proposing who made what at this point, as that is a rabbit hole that has been stuffed with a beat dead horse!
This thread is to gather examples. Thus far I have only observed examples listed above, and would like to see if there are any examples that don't fit that mold.
And again, if you don't have any examples that don't fit into the category listed above, let me know that, as well as how many sheaths you have that fit into that time frame.
Hope this helps

Good point Tom, they are difficult to tell apart.
Look at the Heiser 12-9 posted, The 9 and 6 were probably the same stamp.
The closed numbers like the 0,6,8,9 are difficult to tell. Though the 6 is not totally closed, its close.
It seems that the straighter, open numbers that have definite end points have the obvious serif.
Thanks Tom

samg -that is not a hypothesis, in fact, what you stated is nearly self-evident (with random anomalies).

So then, this is but an exercise to what end?

To what end?
To my knowledge this thread is one that has not been discussed before. A dedicated subject of stamp numbers,their specific style,applications, and trying to determine if there are any variations to what my observations are.
To what end? To see if my observations have distinct variations. So we are all a little more knowledgeable for it.
Had you observed or considered this subject before?

I, as a collector, certainly have -but as much as there are endless variances in all hand-made items -I found it to be immaterial, to the whole.

Sincerely I say, good luck in your endeavor. I must state, for the record, I'm awaiting the "a-ha moment."

I agree, there are always variations in handmade items, I know this perfectly well as I make wooden musical instruments by hand, and not one has been identical.

I think you are making my point in mentioning endless variables. I would agree, but I have not found that to be the case. What I have found thus far is a consistant, intentioned orientation of stamps that have consistent serif number stamps associated with them. No "endless variables" as you correctly put is as it should be. Why don't we see:
1) East facing RMK stamped sheaths with old style serif number stamps, or
2) West OR horizontal facing RMK stamped sheaths without number stamps, or with new number style stamps?

That, to me would be "endless variations". As it is,at this early point, I see NO variation from those observations. I am looking for them.
Capt Chris mentioned that he has some, so we will see.

As to an a-ha moment, this is not the place for that. Remember that rabbit hole you spoke of? I have no intention of going down it.
This thread is dedicated to finding those " endless variables" you mentioned.

.2 here.

Evidenced by the limited photographic record so far, Hesier/HKL used different stamps. One style is far and away the majority, but they did use other stamps nevertheless. They may be anomalies as suggested by Rigid54, but other stamps were available.

Johnson may have used different stamps also. It seems that is the case to this point.