Maybe this will help William
Mike asked when the mid-bead was introduced
The catalog listing from 1895 shows the Lyman front and ivory beads in the lower L corner

A 1903 catalog listing. (Ignoring the fact that looking at the beads and the departing bird doesn't work)

[Linked Image from photos.smugmug.com]

I'm afraid that I can't make the connection between mid-beads and shooting dogs.
Please google "looseness of associations" and the relevant psychiatric disorders.

We've also got a thread going on Trapshooter.com BTW
https://www.trapshooters.com/threads/history-of-the-rear-rib-mid-bead.924695/#post-8988988
Francotte (imported by Von Lengerke & Detmold) and Greener Single Barrel Trap guns were introduced in the U.S. in 1895 and I suspect the ribs had mid-beads.

https://sites.google.com/a/damascusknowledge.com/www/home