I wasn't aware that the U.K. produced cover was welded at the rear, Vincent, and I don't recall noticing any welds when I've had a cover off. I have several examples of the Sten which I can look at and so I will look in detail at the cover. If they are all welded as you say at the rear it must have been found that the metal wouldn't form into the required shape without it i.e. it cracked/split/buckled. It's possible that the profile of the blank included a couple of slits which were then welded up after forming. I also have a Canadianicon made Sten and would expect that cover to be produced exactly the same way as the U.K. cover.