The sticker underneath mine is damaged but readable: made in UK and the date is "1990-09-05", then other numbers one of which a lot bigger which could be a serial number (1391404). I have another model M somewhere, probably a bit younger than this one; they were throwing it away from a govt server room I worked in many moons ago because it didn't fit in a rack drawer. The crap they put there probably broke in less than 2 years.