By recycling I mean the whole barn was used, perhaps moved without disassembling.

I wonder if the newer builders realized the 8' forebay was a stretch and shortened it up. By the way, in the older 8' forbay barns, was the framing material above the forebay lighter that the rest of the barn?

In the newer barns do you see a change in species used and how the timber was cut from the log, different saws, no boxed hearts, quarter sawn and so on? How about layout systems?

Have you checked into what they were farming and how this could have effected the building they utilized.