My wagon has a 3rd row seat, and it doesn't appear to be original. I can tell 2 ways:
First, it is MB-Tex and my interior is leather.
Second, and this is where I'm heading, no headrests on back seats.
Without headrests on the wagon back seat, a child sitting in the 3rd row seat could have their neck snapped violently back in a collision.
My 9 year old daughter loved to ride back there, but I got to thinking about it one day, and what a neck-snapper that would be.
Something to think about.........