Trying to understand the various versions of the Jubilee RD always makes my head hurt, but I found this
write-up that is pretty easy to understand:
https://note.com/aki233/n/n1248c58d9177
It's in Japanese, but using Google Translate makes it quite readable.
I pulled out my 4 Jubilees and the aftermarket adaptor kit from my stash, and think I now get the general drift.
I think the aftermarket adapter kit is a reproduction of Huret part # 2333, which came with some later versions
of the Jubilee RD to make them fit a Campagnolo dropout and add B screw function.
There are NOS Huret part # 2364 bits for sale on the auction site by seller Idealvelo. PM me and I'll send you the link.
These look like they could be modified to look and function like part # 2333.
Also found and purchased a Huret rear dropout.
At some point in the future, I'll make 3D models of the Huret dropout, a Campagnolo dropout, and the adapter kit to
illustrate how these all work.
I don't know how a Simplex dropout differs from a Campagnolo dropout, so all of the above doesn't directly answer the
question, but hopefully sheds some light...