Is there such a thing as a numbers matching AD?
Yes, when the engine serial number that's in it matches the title that that was issued to the original purchaser. Lots of states, and apparently some foreign countries used the engine number for identification purposes. Lots of bolters have encountered problems with titling vehicles they purchased that had an engine swapped by the original owner, or someone down the line. Standardized "VIN Numbers" are a relatively recent thing.
Jerry