Hopefully this will clear up various questions about Conn Directors/student models from 1970 to 1986. This Wiki Article is intended for cornet models only - hopefully I can also start on a Director trumpet and maybe Conn flugelhorn articles, too.
By 1970, Conn was producing two bottom-line student cornets: the brass-belled 15A and Coprion-belled 17A. I have seen several examples of 15/17A/Bs with P-serial numbers, indicating that their production run ended in early 1971. See an example of one here
Regardless, these were the student models introduced in 1971 to replace the 15/17A:
Model №: 19/21A
Where made: Japan
Dates of manufacture: ~1971
Distinctive features: "underslung" main tuning slide, serial number has a dash between P and number, top-sprung valves with partially-visible springs, "Shooting Stars" bell without "U. S. A." on it
The 21A was the same, but with a copper bell. The earliest ones used stock Elkhart bells pre-engraved "U. S. A.", and the later ones were presumably spun copper without the "U. S. A." legend:
So far, I have only seen the above models with P serial numbers, indicating they were only manufactured in 1971. The first image is from Conn's 1972 catalog, and I have yet to see any Conn 16A cornets from 1973 or before, indicating that the 19/21A was, at least, marketed up to 1973.
Around 1973, the 21A was discontinued, making it the last copper-bell horn produced by Conn, and the 19A was replaced: