I've always found it difficult to cross reference the illustration of a particular part and its part number with the way BSA produced their parts manuals. You have to first identify the part in the illustration, take a note of the BSA part number (or list of numbers in some cases), then search for the number(s), which are all mixed up and don't seem to follow any logic - apart from being ad-hoc, on a separate page to find and check you have the found the correct part number applicable to your model.
This led me to make up my own parts book for my own use and relevant only to the models and years that are of interest to me (so leaving out the likes of the Spitfire and export models). It's basically how the Haynes manual did it but they didn't go so far as to give the BSA part numbers (see pics).
I find it so much easier to identify a part in the illustration, note the reference number beside it and to be able to cross reference it on the same page where I can see immediately the name of the part, the models it's applicable to, the number required and the BSA part number. I don't print it but make an Acrobat file of it and access it that way on my PC.
I agree with you, Only some Weirdo engineer would ever organize such things that way ( I know a lot of people like that, their brains work differently than others) And I find early Preunit Triumph books that way,, much improved starting in 1964 on the 650s (63 was a weird crossover) and early Nortons are just as maddening,. One exploded diagram you need a microscope to decipher and then 20 pages of part numbers.
Early AMC Matchless/AJS is that way too and Its a trivia pursuit contest to sort out a Hybrid Norton/matchless (N15, G15, P11)
I used to have shop customers who made up their own names for parts and was enough to push you over the edge.
I am working over the winter to downsize, parts, projects,Photos, tech materials, collections and ORGANIZE! This WILL take time!!!! (Who wants to come visit and help???,, I had a helper for a few months
Dave S,, nice guy but I overwhelmed him and then he found a girlfriend with large breasts and that was the end of that)
I am ALWAYS Looking for MORE tech material though.. and will post a wish list soon of stuff I am looking for. Here is 2 pictures of one part of my office. 1 of 4 filing cabinets (More in the shop) and one corner of my office sagging shelving, I have stacks of paper copies and books I have yet to work on.