Dear Loren and mid-60s Buick "opticians" . . .
Still, it does suggest that Buick applied some sort of extra protection on the front of the hood ornament that wasn't on the back.
I think the reflection of sun light off the windshield would be a more plausible explanation. The extra time/ effort/ cost to apply an addition protective coating to one side as opposed to the other wouldn't be an economical decision upon Buicks part.
Hmm, your point does make sense. It was easier to apply whatever coating on both sides. The extra material would have an insignificant incremental cost.
Alas, the sunlight off the windshield seems unlikely. That energy would only be reflected on the hood ornament for a very brief period of time when the angles matched up. I know these things because my trusty wagon has (among other things) hauled telescopes to weird corners of the world:

My telescope is the yellow one. I'm very proud of the design even if . . . I never did get around to finishing it!

So if I
ever get around to finishing my trusty wagon . . . . I'll still have a few things to do!

That still leaves the fading pattern of 1965 hood ornaments as a mystery. . . . . .

Cheers, Edouard