I was looking at the tt15 and was wondering what points of view were out there???

My TT-15 Top-Single has a full-length under-barrel rib (or maybe a stiffener?) that has come loose. Appears to have been attached with some sort of adhesive stuff. First of all, not sure what this thing does...in fact, it does not show up on any on-line photos that I've found for a TT-15...

I'm curious on a few things... 1. Do only the NEW TT-15 come with the factory adjustable butt plates? 2. It appears the NEW TT-15 stock with the adjustable butt plate is quite different than the gun that doesn't..is that the case? (it looks taller to me) 3. What is the main difference from the...