Well here is my 2c...
Seems history gets muddied over time things left out things added
Here in the UK I run the 912 Register for the PCGB, we had a phone call from a film production company, they wanted some early 911 / 912's for a 'casting'. At Shepperton Studios the director would choose a car for the film they were shooting. So myself and a number of Register members turned up on the day. Tony and his entourage toured the lot and chose my car. They had my car as the principal for 3 months. All the shots you see with Bob driving at the beginning and end of the film were shot in the UK at a Pharmacutical head Office in North London.
(Listen to the alternate ending on the DVD for the actual recorded engine sound, 912 not 911) After all the UK photography was complete they had to find a similar car in the States for all the long shots/freeway.
So, I think its fair to say my car was used for the Bob driving shots and Kurts for the long shots.
Any other car that claims to be used was either a spare or never used for the principal photography.
Obviously non of this is that important, untill someone tries to bump up the price of their car with implausible 'truths'.
Gavin