I have a Txxxxxx 591a1 as well, I can get the details this evening if you wish, not to mention my old Bullpup which is a Jxxxxxx as well, I just have no idea the exact build date.
Received an email from Mossberg this morning. As follows: "Thank you for your e-mail. The date of manufacture for your gun is August 08,2002 and its model 50411"
Serial # is R282xxx