It's fun to guess about what might have happened.  It might help other practitioners diagnose problems.  Is it time here to cherchez la femme?  Dad set up a trust for son so that it would remain separate property and not reached in a divorce?  Son was happily married in 2019?  Not so much now?  What kind of lawyer is telling him to go back and file as if the trust has been in existence all these years?  A divorce lawyer?