The first thing you need to do is recognize that there were 3 parts books for a given production year: Domestic, General Export and USA. For the USA parts books there were two importers: Johnson Motors (west coast models) and The Triumph Corporation (east coac models). Each had their own specificaions for some models. For some years there were supplements specifiying east and west coast iterations. On top of this The Triumph Coprporation issued a multi-page document for each model and model year correcting mistakes made in the parts books. Some of them are 6, or more pages, single spaced. Most of the parts books were prepared long before final descsions on production specifications were made. In some cases this led to chaos.
Then there is a group of years where parts books were printed that contained so many mistakes that they were reprinted. In some manner, or way, the dicarder books found thier way into local salvage houses (MCE comes to mind) that specialized in buying production scrap. Has anyone that is reading this been in MCE's celler? Selling rejected parts, and scrap to local motorcycle trade was a small side occupation for a few factory workers. A lot of these parts that failed inspection, and the odd rejected parts books found their way in to the market only to make the whole what-fits-what, and what is new-old-stock a whole different problem.
Then there are hundreds of parts that share the same part number with different specifications. The classic one is W1332 (37-1332) which has 3 iterations. The other is the tach and speedo bracket 97-1946 of which there are 3 iterations. This is an exercise in itself.
I'am getting a headache, but I have had the same headache for 50 odd years dealing with the way Triumph handled their parts. Where is Jack Shortland, Triumph Export parts manager, when you need him? Passed some years ago. That's why any Triumph dealer "worth his salt" has parts books full of notes and changes.