The mystery is solved if you have a look at the 16H frame and engine number page http://www.wdnorton.nl/Frame_and_Engine_number_page_16H.htm.
There is shown where the only valid Norton frame number can be found.
Any numbers found on other places are either casting numbers or the mysterious additions of either civil servants, military guys or previous owners fitting the bike to the paperwork instead of the other way around.
