Conn gets its own page as the underslung, folded-back tuning slide was used on many models, and these examples are common enough to be had easily.
By the 1960s, Conn was in need of a more modern student cornet, as the 15A/17A Directors were made on the same basic template as older Pan Americans, themselves a continuation of the old 26A from the 1930s. This more modern design with a medium bore appears in Conn engineering vellum (folder 1 & folder 2, for reference), but was first used for Yamaha-made student cornets, owing to the high cost of making student horns.
Type: Cornet
Brand: Conn
Maker: Yamaha
Model: Director
Model №: 19A [21A has copper bell; not shown]
Where made: Japan
Dates of manufacture: ~1971-1973 [1974 - 1977 for similar 16A]
Below is the 1972 Conn brasswind catalog entry for the Conn 19A Director, first designed in the 1960s, and manufactured by Yamaha. This model was made from around 1971~1973, and was discontinued in favor of the American-made 16A by 1974. In 1977, the design of the 16A changed from this underslung tuning-slide model to a more conventional layout.
Here is the full catalog page:
Notice that the 76A Connquest cornet [with tunable bell] is present.