hmmmm, welcome to the forum....
undisclosed location; is it stolen and you are afraid we'll report you?
Not sure how you can assume the frame matches the top, it either does or does not. In addition, to be completly matching internal parts must be numbered. (that was not meant to sound as harsh as it sounds)
I suggest you look over the forum and see what other 1916 erfurts should look like. This one looks fairly okay, the price is a bit high if it is not matching.... not bad if all matching.
Ed