They did, however, note that the seats in question were procured from a different manufacturer and have been used to replace worn or damaged seats on various AA B-757 aircraft.
Perhaps. Any information on the time or number of cycles between seat replacement and them coming loose?
Its possible that the new seats require (but did not receive) different fastening hardware or procedures from the original ones. Its all guessing right now, but I'm sure AA will be chasing this down ASAP. Who knows how many other loose nuts they've got flying around.