Being amused at the suggested simplicity here may be a more appropriate term ?
Suggesting a bike can be identified from just a frame number (without a quoted engine number)(and no picture) in Nortons 'system' is, well, just fanciful ?
The Norton Manuals ALL say to quote an engine number and frame number for identification.
And that was for a factory bike. With 4 decades of possible later modifications to now take into account. ?!
Choppers, hybrids, cafe racers, specials and just plain junk now all come into the account. ?
Folks have been ruminating on Nortons meanderings through the numbering system, for quite some decades now.
Apparently, if you have the journals in your hands, some sense can be made of their 'system'.
But from the limited information released over the years, mere mortals cannot even glimpse the whole story ?
For example, the factory production year ran Sept to Sept, and this has apparently caused quite a few misunderstandings.
Some folks quote calendar years, some folks quote model years, and some quote year of registration.
And none of these may necessarily coincide.
(Did this apply for all Commando production, or did this change part way through ? )
And Nortons apparently, at various times, reserved whole blocks of numbers for a specific model.
This means that, for example, an ES2 number would be followed by another ES2 number.
But this may not have been built until months later - or whole blocks of ES2 numbers were built months later, with seemingly sequential numbers.
And bikes requiring rework were put back into the system, and numbered when they were finished - so sequential numbers may have been months and months apart.
Its a minefield out there.
Without a picture, and serial numbers, could be calling an apple an orange....
