Here are the Conn tunable-bell cornets, trumpets, and flügelhorns. Notice that the 14/18A cornet is the only cornet we'll include from the student-level batch as the bell-crook slide barely functions as a tuning slide, and later cornets like the student 15/17A and professional 5/9A have a removable slide that is barely a "tuning slide". Both aforementioned groups had main tuning slides elsewhere.
First, here is the main Conn cornet with tunable bell:
Type: Cornet
Brand: Conn
Maker: C. G. Conn, Ltd. [Conn-Selmer today]
Model: Connquest
Model №: 76A
Where made: Elkhart, IN, U. S. A.
Dates of manufacture: 1961 - 1973 [approx.]
This design of Conn cornet was one of many that were discontinued in the early 1970s, as the 1979 Conn catalog shows just one cornet model, the student 16A. The 78A "Century" model, the Connquest's intermediate replacement, was added in 1980, but the number of Conn cornet models didn't change much from 1985 onwards.
Here is the full catalog page:
Notice that the 19A Director cornet [with underslung tuning-slide] is present.
This even goes back to the Conn & DuPont First Class model cornet, circa 1879:
Type: Cornet
Brand: Conn & DuPont
Maker: Conn & DuPont [Conn-Selmer today]
Model: First Class
Model №: [N/A]
Where made: Elkhart, IN, U. S. A.
Dates of manufacture: 1879-1880