Frame ID numbers

I have a couple of 850 Norton frames and the numbers are : 850 F101154 & 850 F112311 . I can't find any information in the literature on what these numbers are for as the frames are registered to the ID tags. Can anyone direct me to information on the purpose of these numbers ?
Thanks Robin

They look to be frame numbers applied to pre MK3 850's, mine has one and they bear no relationship to the engine number or the same number stamped on the indentification plate.

Not an all inclusive survey ... A thorough VIN registry was not my goal, but to see a pattern of which were wide or narrow rear loop frames, as it relates to fastback tail section compatibility.... Cutting the frame loop seemed like so much butchery to me.... I ended up making a wide fastback tail section mold to end the matter.

http://atlanticgreen.com/commandoframes.htm