Er kmccabe56, the answer to your question is right up there in post #2245 of this very thread!
Slightly different cutout shape of the trunk mat for convertibles, IIRC.
Like I said: Lazy. You know how crowded things are downstairs and I just didn't feel like shifting 3-4 piles of stuff to get into that shelf to look. Interesting that somebody finally decided in 1966 that V needed a different floormat than L. I take that to mean that the pre '66 floormat was a mouthful in a V trunk?