Does it have to do with the one style used on the Cougar headlights vs the Mustang headlights? I thought that there was a higher capacity breaker in the Cougar version.
Yes, the headlight switch is different on a Cougar for the quad headlight draw.
The knob, bezel, and nut should all be the same, on the headlight switch assembly for Mustang and Cougar.
Remember, starting in 1968 interior components started getting smoother, less sharp, more flush mounted, and overall safer for the occupants.
These 1968 knobs are more rounded on the surface.
I would also agree on a supplier change or design change to save pennies. Less metal costs less money and adds up when talking about numbers in the 100,000's of units.