1964-1970 Mustang Horns Differences?

[KR Convertible]

The 2 circled together don't look like a matched pair.  The one without paint looks like a 65, but it's hard to tell because the circle goes right over the mounting  bracket. 

I believe 65s were the only ones to use the depressed circle as a key to locate them. 66 went to the bent finger.

Any dates stamped inside the openings?

[Kent]

In the beginning of the thread are the pictures without the circles maybe you can see it better there. The other 2 in the other picture below are not identified at the moment also. They could work on a 69 Mustang but they have a different bend of the bracket.