A 40 year period is really a short period of time. A generation, 20-25 years, I am two generations old. If I look back through my life a lot has happened but the surrounding land scape, buildings included has changed little. The houses that were built in the 60's have change little as well. We are approaching changes that will be more noticeable.

I suspect you may be looking too hard for a reason these newer building exist. If you applied the information you do have to a timeline, frame types and such, along with habits of the people, farming info, other aspects economies and such, what picture develops?