I'm a bit confused by some of the terminology here. Although they differ physically from manufacturer to manufacturer I believe that all the issue knives are "Knife, Survival Type D"'s. Before they went over to the NSN, 5110-99-127-8215 the codes (for the same Item) were
Army 1B/4594
RAF 27c/2360 and
RN 0274/4594
Saying that some way to differentiate the two obvious variations, the earlier (better) ones with the convex blades and bolt on handles and the later ones with the poor steel and big copper rivets is needed.
If I'm wrong (more than likely) please pull me up as all I'm going on is Ron Flooks book.
I realy liked mine, split no end of logs with it back as a student.
ATB
Tom