Last week I found a copy of a circa 1980 Selmer Paris brochure. A very useful item, in that it lists the cornet models that were available in France at that time.
The last year a K-modified long model cornet was listed on Selmer US price lists (according to the info on the lists at saxophone.org), was 1978. After that it seems Selmer Paris cornets were no longer for sale in the US.
I'm posting a scan from the brochure listing the models, then photos of each of the models from my archive. Here's the English translation of the info from the brochure on these models:
352 - Cornet in Bb, model 43
354B - Cornet in Bb, short model (which is what I believe is shown in the brochure photo)
353B - Cornet-trumpet in Bb, American model (the cornet that was produced after the K-modified)
353C - Cornet in C, with slide for Bb (directly translated, "echelle" is "ladder" in English.
I believe there may have been a period of time (mid to late 1980s until late 1990s) when Selmer wasn't making cornets, just focusing on trumpets, until the Concept cornet began being manufactured.
Here's are the photos of the brochure and the various models mentioned: