I really appreciate the help, I may not be following right, or may not be explaining clearly, so I did a quick image to help illustrate what I'm confused on.



Here, we have a simple, yet beautiful (humor me) double-width tartan that will be used to make a kilt, it's taken in half, and rotated to be joined. However, the selvedge doesn't contain the same portion of the tartan, which would not look good, if sewn up that way.

Does this happen, requiring a hem with double-width tartan, or is the fabric woven in such a way that both selvedges are the same?

Hopefully that helps explain my confusion a little better.

(Edited for proper image code)