There might be some date confusion.
Marty's original post was about 4/29/1968, F70x14 or FR70x14. This would presumably cover the late 1968 Mustang GT models.
The original post also for comparison stated that they were on his 67 GTA (F70x14).
Finally the original post stated that his 68 Shelby GT350 (12/2/67) shows them as an option on the Marti report.
Bob's reply was in regards to the 1967 model year Shelbys, and stated that they did not get them from the factory, and would want to see evidence. Perhaps Bob missed the dates - there was a lot packed in that little paragraph.
As for MCA Concours, and this 4/19/1968 brochure, I think (opinion here) that the judges that knew/know about it are in the minority, and would not likely be caught. Then again maybe it's just me in the minority because I did not know. However, this sort of education would increase the percentage of those in the know.
I'm sure that Marty posted this to get some discussion going, perhaps finding someone with a Marti report, original owner car, etc. to back up or dis-prove the memo.