The key to understanding my view of intent lies in the distinction between reference and sense. For example, the sense of the word "speech" is an abstract concept. The abstract concept has many potential concrete referents, such as verbal speech, written speech in a newpaper, electronic signals broadcast over radio, etc. My contention is that the word "speech" in the First Ammendment must be understood as the abstract concept "speech," and not as the set of all referents known in the late 18th century.
Under your view of intent, how do we deal with words in the Constitution which the authors misundrestood?
The same way we would deal with such situations in contract law. A contract binds you to the normative sense of what the contract says, not what you may have thought it meant in practice. A contract or a Constitution defines the "rules of the game," not just the specific plays that will be made in a specific instance of the game (although those who write the words are usually motivated by such past specific cases.)