dating amc pre-commando gearboxes

Hi all. I am putting this question here as it pertains to at least pre commando nortons and matchlesses with an amc gearbox.

I have seen a lot of discussion about changes in the amc box and to what extent the earlier gearbox parts are useable in a commando box but I don't recall seeing and could not find a list of the approximate manufacture dates of various amc box serial numbers. THis would be helpful to match pre commando gearboxes to engines and frames. Does anyone have this information? Thanks in advance and let me know if you think this should be somewhere else on the forum. M

AMC gearboxes were not fitted sequentally, rather they were made in batches. Numbering was consecutive, not interleaved, because the internals were identical.
Production spans two intervals: 1956/57 -- 1961/62 (N and M prefix serial numbers) and 1962/63 -- 1968/69 (NA and MA prefix serial numbers) .
In the former group, about 30-40 gearboxes a day were made. In the latter, output dropped to about 10-15 gearboxes a day. All gearboxes were manufactured and assembled in the Plumstead works.
You can estimate the yearly production based on the serial numbers of bikes, for which there are tables.
So, for the 1956/57 season, serial numbers may have started with N1001, M1002, and by this, you can estimate the serial number at the start of each model year (Sept 1st).
For a better correlation, you need to review dispatch records.

- Knut