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My bad, thought I have a 1979 US Divers Catalog with the Calypso VI already offered, but now it seems it is a 1980 US Divers Catalog, just the Copyright on the Front Page is from 1979.......8I don't see any external difference between the Calypso IV and the Calypso VI. Even the yoke and yoke screw look the same heavy design.
I actually never notice there were two different labels... I probably thought the "VI" was just a typo (or I might have even reversed it in my mind without noticing). I don't remember ever seen a Calypso V, but I don't have catalogs for 1977, 1978 and 1979. In 1976 there is a Calypso IV and in 1980 they show a Calypso VI. I don't know when it actually switched.