It's definitely not Black Watch. Black Watch has an A-B-A-C repeat, with the B and C blocks being different (one blue block has two double black stripes, like this tartan has, but the other block has a single centered double black stripe). And the green block in Black Watch has only a single black stripe, not a double one. And the proportions are wrong - the green block should be proportionately smaller.

The picture looks like the piece doesn't have a kilting selvedge. So, the white thread is a moot point and would be hidden in the hem that you'd have to put in this kilt.

Could make a nice kilt with a hem!

Barb