Two-step blackout blindstitch

I did another remake last week; a repair, actually.
These blackout-lined silk panels were sun-damaged and the homeowner wanted to cut off the damaged part and re-hem the lead edge sides.

A few weeks ago I was experimenting with a way to hem drapery lead edges without pinholes of light coming through the blackout lining.

This was a perfect chance to practice and test my idea.

The return edge was undamaged and didn't need re-sewing, so I did the flashlight test (the only test that is definitive) on the original machine blindstitching, and the result was a lot of bright light coming through each stitch hole.

But on the lead edge, with my stitching method, there was zero light.  Yes, there is a flashlight directly behind the stitches in this photo!- and I'll prove it, at the end of this post.

I used a blind-stitch variation: the same stitch I learned as a girl for hemming skirts.  But for these panels, I made the stitches about 3/8" in from the edge instead of right at the edge as I first learned it.

First I folded two layers of blackout into the side hem along with the silk.

Holding the lead edge folded back, I started a stitch in the fold:

Then dipped down and about 1/8" over to take a stitch in the face/lining:

This creates a staggered line of stitches along the hem, which I'm calling my two-step blackout blindstitch.

Where the needle has made a hole in the blackout, behind that there is another layer of blackout to keep the light out.  When smoothed back down, the lead edge hem is neat and clean.

When I pulled the fold back and did the flashlight test, there was light at every stitch:

Then when I let the fold lay back over the stitching, the light disappeared!