Unique speedo cable?

I did change out a speedo cable on a 66 Barracuda with a 67 model cable. I found the 66 Cable was close to 4" shorter than the 67 cable. I purchased a new replacement cable from National Moparts for a 67 as 66 was not in stock and that replacement cable was very close to the length of my original 67 cable. The ends were correct and so was the grommet they supplied.
I figured the length difference was due to early A to later. I didn't realize they should be the same part number.
I garbaged the original cable so I have no part numbers.