Between about 1971 and 1978 just about every Cobra, 427 Cobra, and any version of Shelby prepared Mustang part had been reissued and or reproduced both FOR THE FIRST TIME. Maier Racing, Valley Ford Parts, Cobra Performance, and others tended to specialize on certain models.
From memory none of the people commissioning new made parts were trying to pass them off as assembly line parts. I knew or talked with some of them back then, friendly fun loving people for the most part. There was a demand for Shelby everything and they filled the demand. Customizing Mustangs (or any Ford) with "Shelby parts" was big business and as the Mustang Club of America developed out of a local Atlanta Mustang club and SAAC condensed Shelby related clubs under one roof so to speak the demand got higher.
By the mid 1980s the second round of reissues and or reproductions was well under way. In 1984 I was visiting with one of the shop owners that commissioned dozens of new “Shelby” parts on his own. That day in January 1984 I sat in his office and he showed me a sample of his latest reproduction. It was his version of C3RA 427 Cobra 2” round “COBRA” mascot emblem. He had a sample of a freshly made one and the “old” one he had copied. I laughed and told him he just reproduced a reproduction, i.e. his “original” was an earlier reproduction a company in California had made. He shrugged his shoulders and indicated it wouldn’t matter as customers would buy all he would care to make. Since then I have seen a reproduction of that reproduction.
Just because (insert anybody’s name or relationship) has had part X on the shelf since let’s say 1979 DOES NOT AUTOMATICALLY MEAN IT IS AN ASSEMBLY LINE PART. Tiny wire clips to COBRA intake manifolds and everything else you can imagine has been replaced by new product at least once since the 1970s.
Another "Shelby" issue, especially for Cobras, is that many of the parts used to build new cars would not have been the same thing you got through the Shelby American parts department or a Ford dealer for service. I will use ball bearings as an example. AC Cars used British made bearings and suppliers to make the cars. Shelby American offered bearings made for the same jobs but made in America and sometimes by different companies than AC Cars used. Even official Bills of Material and service part books have to be used carefully if originality is important. Street and race SA often used one thing and sold something else for the application.