Troy, Bill, Hohner had several melodicas on the market in 1975. Bewteen 1970 and 1980 they had several great melodicas selling including the professional 36 and the piano 36 which many Jazz musician were using. For the smaller melodica the Piano 26 and 27 was a nice upgrade from the starter soprano and alto student models and were were very popular. If you had the extra money at the time you could opt for the Cassotto which was considered the top of the line for the smaller melodicas. I would actually to find one for myself. I recently found a Hohner Solist that is probably in my opinion the best of the best from Hohner. A single reed melodica. I agree with Troy, for a fast responce I like my Hammond Hyper made by Suzuki. I do not own a Yamaha, though it has been on my (I need to get this one) list. Troy has mastered the art of the Irish reel on the Yamaha so there is no better person to point you in the right direction for right melodica for traditional music.
For a long time I have been trying to get some kind of history of the Hohner melodica line but only find the same information repeated and no actual time line.