Of course, it could just be a weaving error, but either way, my hunch is that the selvedge is under that blind hem stitching and you could proceed with your plan to let it out.[/QUOTE]

From the photos it does appear that the cloth has a selvedge. As has been noted, the sett at the selvedge is truncated with the black being narrower than it should be. I don’t believe that this was an intentional selvedge pattern (pattern, not mark) but a weaving error. That might account for the reason why the hem was added - to hid the error. It might look better if pressed hard but as viewed it looks bulky and ungainly.

IMG_3259.jpg

It the hem was unpicked and the cloth pressed out then the selvedge would look like the central section I've reconstructed in this image.

IMG_3259a.jpg

So, it looks like it would be possible to unpick and lengthen the material but it will result in a visual error in the cloth. Nothing wrong with that, especially if you are able to explain the anomaly if ask. Remember that it you do unpick the cloth then the kilt will be a little longer that currently and so you may wish to have it correspondingly shortened at the tip.