H4, H18, the times I've seen the H4 bag in a Turbopower2, 3, or 1000, is too many to remember. I blame Hoover, as I think they should have used the H4 bag in all cleaners marked 'Turbopower' or better still redesigned it to look like the H18 and sell that for all models - which of course is exactly what Hoover did do in later years, seeing how the plastic tube of the standard dirty fan Turbopower was a perfect fit for the diameter of the H18 bag.
Mr Murray, I know very little about the actual production of anything, but it would be a strong suggestion on my part that the belt guard you have dated to 1992 may well have been part of a current batch at that time. There is nothing to say that Hoover didn't have thousands of them produced at a time. Not only this, at a stretch we could even say that the part might have been made in late December 1992, whilst the hood was made in early January 1994. If you include delivery times and whatever else, that means there may potentially have been only a year or even less between the two parts coming into stock at Hoover. Generally, I would not be surprised to see date stamps of parts on a cleaner which differed by a year or two. Mind you, I have no idea as to why some parts are stamped and others aren't, and what purpose it served anyway, because I am sure as sure can be that back in the early 1990's the Hoover engineers did not sit around discussing the possibility that in 20 years time we'd all be sat at home wired up to the 'internet' and discussing their products! Can you imagine?