Kawasaki have the same numbering system in many of their parts and accessories. They use both the Showan and the Julian system for date identification. Kawasaki also use alphabetic letters to represent the months for example they use a 7 to represent the year 1972 and lets say a C which represents March so on a part one would see 7C. One thing about Kawasaki is they don't just use from A to L. I understand they use other letters. I'm not so well versed with Kawasaki other than I own 2 x 1972 Z1s and a 73 Z1 and I can navigate my way around these identifications. Kawasaki switches are identified using the Julian calendar plus a numeral for the month i.e. 4.4 in Kawasaki would represent 1974 April, their swing arms are also stamped in a similar way One of my swing arms is 3.3 being 1973, March.
Would seem to me that probably the parts suppliers made the decision as to what method they would use. The one item I cannot fathom on a Honda is the coding on their brake disc and the stampings on the rear shocks