Just to confuse things a bit more, or possibly throw out for discussion something that is completely wrong, I was talking to an owner of one of the cars that has a kardex Ausgel.am date of July 1965 but a 66 paint badge. It struck me that given the car probably would have been completed up to a couple of weeks before the Ausgel.am date (as that date is when it left the factory and earlier records show some time between when cars re finished a per the build book and the Ausgel.am date) and all of the features apart from the paint badge are pure 65, that those last few cars produced late in June 1965 MAY have had 66 paint badges put on them to "make them look like new(er) model cars". The same sort of thing happened at the end of June 1966 when the last 20 to 30 cars became the "Deluxe" cars apparently to freshen them to compete against the newer model or otherwise get them sold.
We have to remember that Porsche were in the business of selling cars and newer model cars always sell better than old ones. So maybe the 66 paint stamp at the back end of 65 production cars (I have a 66 code appearing as early as car 301945 which went to Sonauto but Porsche documentation says was an August 65 car). Interestingly all of those 66 paint stamp but looking like 65 cars that I have kardexes for (or other data signifying a Ausgel.am date) show them LEAVING the factory in late July or early August.
To be complete however i also have some 64 paint badge cars leaving the factory in early, and in one case late July.
However i am wondering from all of this whether a 66 paint number, at least for the earliest cars, is a reliable indicator of a change in "model year" when all of the other features of the car suggest 65?