All metal stems were quite common in French bikes in the 1960s & 1970s bike boom. They weren't fused to the inner tube. They had a flange base that was inserted in to a pre cut hole in the tube and then a washer and threaded nut was run all the way down the stem to clamp it in place. My guess is you could at one time buy inner tubes without valve stems and reuse your metal stems. Post ww2 had some major economic effects in some European countries and this is just the sort of savings I'd expect then. Metal based valve stems wouldn't sit well in narrow rims and would get tiny bulges on either side of the valve and blow out inside the tire.
I had a valve stem blow apart like the first photo in post 14. My wife and I rode our tandem one day last year. The next day I found the front tire flat and the part of the stem laying on the garage floor. Just happy it didn't blow while we were riding. Perhaps there was a bad batch of tubes from some factory.
bolted in metal stems are the norm on aluminum automotive wheels where the metal is just too thick for the press in rubber stems.