Are you referring to the Jaggies or stair steps you can sometimes see in the alignment of the Tartan lines? Where one line does not line up perfectly with the next.

Or are you referring to a shift in the fabric over time that could be caused by uneven tension of the hand sewn stitches?

Or perhaps an un-evenness of the spacing of the individual stitches?

I'm sorry to ask for so much clarification but as a kiltmaker who strives for perfection I would like input from someone with your background.