I think that it is very good to now include examples of bikes without head badges, as they seem to be a significant portion of many serial numbers projects.
Interesting newest examples show that in addition to the N-300,000/N-400,000 series (say below 450,000) there are also some P-400,000 series examples (above 450,000?); [and there are some P-500,000 examples].
What may have triggered the switch from an “N” prefix to a”P” prefix, from about the middle of the 400,000 serial numbers?
And how many bicycles did Shelby actually produce in one year (which years?) and did Shelby round-up its stated capacity to 200 thousand per year?