Difference between 67S and 68S rear view mirror

Looking for a little input from folks with original/unrestored cars.
I always thought the only difference between a 67S mirror and a 68S mirror was the brackets, ie chrome screw in for 67 and silver breakaway for 68. I thought that the black plastic pebbled finish mirror bodies were same but now Im not so sure. I have two different bodies that at first glance look the same but upon closer examination have small differences:
the 67 day/night tab is a flat while the 68 is enlarged/thickened at the bottom. Also the solid plastic band that trims the mirror (non pebbled area) is thinner on the 67. I have attached some photos to show the differences. Any input would be appreciated.
Thanks,
Skip

I have both - definitely different in mount, stem, and mirror.

My '67 mirror has the 'flat' handle, and I believe it is original to the car. (305811S)

Thanks Guys, the 67 units are scarce as hens teeth. I managed to destroy the one I have in the photos. It was extremely brittle and practically disintegrated when I tried to remove the glass. Further research suggests letting it soak in water for a few days or in boiling water for a couple minutes might make the plastic less prone to falling apart. Im going to try the water technique this weekend on the remains of the mirror housing and see if it really makes any difference.

So much for boiling water. Had no effect, still VERY brittle