This is what I know about this part naming system. During WWII the US military were dismayed at the number of parts and different systems for naming them that they had to stock to keep the war machine going. Ford had their own system that had the central numbers preceded by an alpha numeric prefix and if there was more than 1 there would be several alpha suffixes as in C1AZ -6731-A. This was the oil filter used in mid 1965 model Mercury and Ford cars. 6731 stood for an oil filter. C was for 1960 to 1969 the 1 was initial issue in 1961, AZ was for all models. The suffix at the end indicated there was only oil filter from Ford under the 6731 number. That system was developed in the 1930s. Ford was one of the few that had an organized parts system at the time. The rest were a hodge podge of alpha numeric numbers. So the US military procurement grew weary of this hodge podge and proposed several solutions. One was the GM system of 7 numbers. All I know is certain parts started with 1 (starters and generators for example), others started with 3 3tc. Then there was another system that was adopted by IH and Massey Ferguson. JD had their own system and did not change it. To this day you have no idea of what the part is by the number. I am most familiar with the IH and Massey System.
The original system invoked at the end of WWII for IH used a 6 digit number followed by R1, R11, R21, R31 sometimes R41, and the usual R91. the R stood for two things R meaning revision 1 2, 3 as IN R1, R2, R3 etc. R11 usually stood for two piece assemblies. I think the R21, R31, and R41 were revisions to R11. Then the R91. The R91 referred to a part where there were several R1 parts composing all the parts in an assembly. So a 6 digit R91 assembly could have a dozen or more parts constituting the R91 assembly. IH also used the 5 digit designation for bolts and nuts and later on for whole parts. And IH would allocate batches of part numbers to the individual plants through the bills of material they were using. For instance the Tractor plants got numbers starting with 350000R1 in 1946 and continued to about 409000C1 in the early 1970's. The tillage people got numbers in the 450000R1 up to 550000R1 .Doncaster got 700000R1 to 750000 R1(I think). Hamilton got numbers for drills etc starting at 800000R1. Melrose Park got numbers in the 250000R1 to 349000R1. Not sure of trucks but I think they were in the 100000R1 or 200000R1 or construction equipment. So to an old hand like me I could tell you that a part with the 354000R1 was probably used first in about 1951. Similarly 368000R1 was first used in about 1958. And so on. By 1970, IH had gone to 7 digit numbers usually starting with 3000000R1 for the European produced tractors. They always had used the 1000000R1 for publications such as operating manuals. This was getting unwieldy so IH adopted the C designation (change) instead of R designation in the 1970 period. With the proliferation of parts in the 1970's this system lasted about 10 years before they were back again at 7 digits. By the Tenneco takeover the system was changed again to A(alteration). and the 91 designation was dropped So early Case IH parts had 6 digit numbers followed by A1, A2 for a revised version etc. When the CNH merger occurred the New Holland (FIAT) system of 8 numbers or more was used to get away from the confusing array Case and David Brown had brought to the mix of part numbers
Massey-Ferguson adopted a similar system and they are still using the M (modification) as in 357323M1. Simply put they had many fewer parts than IH of Case IH had.