Much consists of heavily intertwined threads woven at various times by various people. This makes a fascinating study in its own right, but like many things, you have to spend a lot of time and effort on it. Careful reading and comparisons of many of the older books will clear up many "puzzles" in regard to artificial flies. The unprecedented access and manipulation capabilities we now have in regard to all sorts of information makes it possible to compare and collate all kinds of things, make connections, "educated guesses", and draw often quite inescapable conclusions from the material at our disposal. This is something no authors or anglers of former times were able to do with any notable degree of efficiency, and the vast majority of anglers only had access to local information anyway, and usually severely limited information at that.
Will it help you to catch any more fish? Almost certainly, in the sense that the more information you have the better chance you have of exploiting and capitalising on it. But, at least in regard to artificial flies and their antecedents, it is primarily the pleasure of researching and learning about our angling heritage.
With regard to Iron Blue Duns, you will note that Walbran refers to various insects in that book using both the old and the "New" nomenclature, ( To whit, the "new" nomenclature which refers to the sub-imagines of ephemeropterans as "Duns"),
http://www.archive.org/stream/fliesangl ... h/blue+dun
( Click on the orange "Search tags" at the bottom of the page to find all references).
Other people got ( and still do get!), badly hung up on this, notably Skues and Halford when trying to solve the "puzzle" of the "Blue Dun" which they could not find and could not identify. It is my contention that they and many others who commented on the matter were unable to solve it because the "Blue Dun" is in fact a grey sedge ( Gray Caddis in "American"!

). The "Dun" part of the description refers to the "old" insect class as "formalised" by Theakston, although the descriptions he actually used were in common use and had been for a very long time among anglers. This also explains the stylised "tent" shape of many wet fly wings, which bear no resemblance at all to the shape or behaviour of ephemeropteran ( "Mayfly" American), duns, but are an excellent imitation of sedge ( Caddis ) wings.
This also has ramifications if you are researching patterns to see if they might be any good, or what they are designed to represent. A "Brown Dun", in the "old" nomenclature is a brown caddis fly. A Dun Brown" is a grey stonefly, and there are many other examples. This is of lesser importance to fly-dressers who dress their own flies to match naturals, but it has far reaching effects on commercial dressers and others who "dress to pattern". Unless they are aware of these naming conventions, and few are, those who copy or buy and use the flies to imitate something or other, are using something which wont work very well, because it was simply never designed to imitate what they think it should!
Many modern fly names are based on the "old " nomenclature. The Blue Dun being a case in point.
I can't remember whether I have told you before, but a small Stewart' s Spider dressed with purple silk is usually very effective for Iron Blue hatches, and due to its construction, may be fished in various ways to match the stage of the hatch.
TL
MC