I recently bought a house with an original structure that I can say definitively is pre 1850. It has several additions including a 1950s a 1980s and a new kitchen wing in 2000. On the side of the 1850s section is an addition that appears to be late 1800s in style, wood flooring and nails, and other little details. However when I had the house inspected the inspector was quite insistant that this addition was added in 1950 along with the addition on the other side of the 1850 section and that the owner just made it look old. His evidence was that the floor boards were of softer wood than the same type of floor boards in the bedroom of the 1850s section. He did this by sight and didn't bend down to feel the floors to confirm this. The inspector specializes in old houses and seemed very knowledgable - but this addition feels very old.
Besides my curiousity, this section has a very small stairway from the first floor to the second. I am updating the bathroom in the second floor and would like to get rid of the stairs to gain more space. If this is a fiftie addition then I have no problem - if 1800s then I won't touch it.
My home is in Bucks County PA and its a classic simple PA farmhouse. I have a hard tim believing in 1950 they would go to the trouble of making an extension that looks and feels like an old home...