Obviously I don't think its simple.
Knowing Clair, he'ld be aware of the difference between an original '67 seat and a '68 or '69.
Archival evidence is good, but when there is archaeological evidence that appears to call it into question, its worth examining further. A reasonable possibility is that at the time of publication bench seat headrests were not available. At some point subsequent that may have changed. When Clair checks in he can fill in what he knows about the car.
