When this full exhaust was released, it was composed of a kit with the 1199 upmap only... in fact it initially came with a Sprint filter.
The slip on was available for the 899 with a model specific upmap as was the 1199 slip on kit.
When the 959 and 1299 was released, Ducati signed an agreement with Akrapovic to become the DP supplier and kits were sold specific to these models. In response, Termignoni developed the front exit exhaust and the rear exit model was pretty much at end of life and was not intended to be sold as separate components... possibly a licensing deal with Ducati since they were only available in the US from Ducati authorized distributors.
However, I suppose that through various purchases, installs, and for what ever reason, some of the original kits are likely floating around and since the headers of the full systems mate with any Panigale model, they can be fitted to remove the cats on the 959/1299 and Euro 959 to replace the cats and side exhaust.
Since this was not really intended to be marketed to the latter bike, I would imagine that Termignoni is focusing their efforts on the front exit.
I don't want to put words in
@CB519 's mouth, but I suspect that this kit initially came with the 1199 upmap.
https://www.pure-ducati.com/p-5038-ducati-1199-panigale-termignoni-full-exhaust-96480141a.aspx