And the interesting thing is, both years use the same wheel opening moulding on cars that didn't have fender skirts.
Soooooo........, with that in mind, it must be either the holes in the skirts for the trim, or the latches for attaching them that differs from 65 to 66.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
Ive added two pictures. From all the pics ive seen lately one difference and it may be the only one is the size of the tab of metal to support the trim is larger .