What you guys fail to realize about shelby cycle company as well as most other smaller bicycle companies.... they used what they had. They weren't a huge seller like schwinn so frames were left over and they used what they had sitting there. You're telling me the person stamping serial numbers stamped one bike per order? No, he did as many as he could in a days shift. As fast as he could.
So how do you possibly date a bike by its serial number yet the parts on the bike weren't even produced yet or even have a patent applied for yet? It's like saying you had a 1936 Shelby with a Shock ease fork that wasn't produced until 1940/41. Understand? Look at the patents. Simple as that.
Artist renditions in ads are no better than a police sketch of a suspect. You can describe to the artist what you want, it doesn't mean that's exactly what you're getting. It may be similar but not exact.
Lastly catalogs and ads are not the final word. Anything could have been ordered back then if the parts were available. No different than wanting a car with leather vs. cloth. They'll build what you want if you pay for it. Paint, options, you name it.