Hello again James. Well the Electrolux 502S, 345, and I think 550 all became exclusive lines after being discontinued. You can spot the exclusive 345 a way off as it had a soft moulded grommet on the mains lead to stop it being fully wound into the cleaner and it came with a moulded plug too. As I am sure you know, this is not like other Electrolux cleaners which had a hard plastic grommet which could be unscrewed from the lead and rarely had fitted plugs. The 406 was always exclusive to Co-Op, I think they may have had stock held over. There was also a basic Twin Turbo and Slimline cylinder which went with the 406 as a Co-Op range.
The reason that 1990 comes to mind is because a Co-Op food store near my shop was extended and they opened a large electrical department. My step-daughter as she was later to be went to work in the new store as they needed more staff. She was not on electrical and only as a Saturday girl. She turned 17 in January of 1990 and this was her first job which is why I remember it. Well my point is I remember going in to see her and of course to see what cleaners they were selling. One of the cleaners was a 406 and I don't remember seeing it there again the next time I went, which would have been only a few months later.