Cant find my most up to date parts book but the one I have in front of me shows two part numbers for the primary gear but they are the same for the r and sp for the relevant years (if that makes sense) If you look at the clutch basket gear that it meshes with the part number doesnt change for the r or sp through the years so it must be basically the same gear.

Honda part numbers are made of three parts xxxxx-xxx-xxx (some have two more digits for colour code) the last 3 digits refer to the modification and sub contractor designation. So the different numbers could just mean they are manufactured by a different company or have a different treatment process.

That said the last digit of the first part number changes as well, my manual describes that as the function and component number???

Anyway time to take my anorak off!