James;
Thank you very much. I have some additional info from my brochures that I will add.
1) I have an example of an "older" version (jodhpurs and jacket) that is exactly as you describe except it has 3-41 in front of M.J.O'M.CO. PRINTED IN U.S.A.
2) I have 2 examples of the next one that is exactly as you describe except it does not have any print date at all after PRINTED IN U.S.A.
I was also pointed to this post from 410bore (Kris) that showed the differences in the wording of the SAFTEY paragraph but I don't know the print dates for those.
Helpful Hints Pamphlet Variations
Were the first ones put in the registered magnum boxes maybe?