but I so often hear it used to mean "big old house with lots of rooms and maybe a porch" for houses built as late as the 1920's!

We're not sure there was ever a porch on the front of ours. We're pretty sure the sunroom along the side was built over from a deck at some point, but again we're not convinced that was original. The internal structure of all the rooms has been pretty heavily rearranged.

That said, someone came tonight and looked at the place and said all sorts of effusively complimentary things, so yay for that.