I'm just going to offer my opinion. Feel free to disagree. But I studied this very closely over the years. The bottom seam you see is in fact a single join seam between the backing and the front material. The reason it is visible out in front in the reference photos from the traveling displays is due to SAG of the backing material and the filler inside the original vests (which are very old!). The sag has caused the bottom seam to be exposed over time. The seam originally was not visible from the front. You will not find any photos from any of the original film shoots in 1979 and 1982 which show that bottom seam visible in the front like that. And also, the backing material (inside of the vest) on the original was not any sort of reflective or shiny material. It was a heavier cotton material -- another reason for the sag. so for it to be accurate, as far as SE, it has to be a sagging seam, where the backing material is sagging, not an actual seam that goes all the way through from front to back at the bottom (creating a lip) like I see on the MOW vest.