I called SD yesterday. Their explanation, not mine, is that the fender portion of the "early 67 stripe, has only two stripes instead of three".
That's their wording. Granted that they have so many products offered that there is a lacking in expertise on each specific one.
The actual explanation is highly likely what I said previously, that it has to do with the application of the stripe with no center stripe on a 67 between the logo and the edge of the fender on the door side. I suppose that was too complex and perhaps esoteric for the SD Tech guy to explain?
IF that is the case you can use the 68 stripe and just eliminate that portion of the stripe in the installation.
That as I remember also un-centers the logo on a '67?