1973 - 1975? Check out this Date Chart
EDIT: After looking at it again and again once more, I go along with David's thoughts above. I too am thinking that some of the Tang marking has been obliterated. The "triangle" in the chart is a distinct triangle whereas the one on the tang has straight sides toward the base of the triangle. I don't have it in the house but later, when I'm out in the shop, I'll look at David A. Krauss' book "American Pocketknives - A History of Schatt & Morgan, and Queen Cutlery" to see what he has to say.
I went ahead and got Krauss's book from my shop.
The chart posted by Duncan in his post above is I believe from Lavona Ferguson's book "The Romance of Collecting" and is Apendix A in Krauss' book. There is also a similar chart in Krauss' book on page 87 but I can't post it as I don't have permission. I can now say that Krauss says in his book that the chart represents an effort by many to make some sense of Queen's tang stamps but is not definitive.
On page 85 of his book, Krauss says;
"One must note that there are some serious difficulties in attempting to set out a definitive chronology of Queen tang stamps as there does not appear to ever have been an iron clad, consistent system of stamping. The company might have used an older or a more modern tang stamp for various reasons, ranging from convenience to specific requests from private contractors or knife clubs. It has therefore utilized different tang stamps (and sometimes no tang stamp at all) at different times. Additionally, as is true in the example of the doctor knife, blades might be used on the same knife which has been manufactured or tang stamped at different time."
Note: There is a picture of a Doctor's Knife on page 85 with a blade etch but no tang stamp (courtesy of David Clark).
