Independently verified. Markey is the named sponsor of record of S.1616, the Judiciary Act of 2023, which he introduced in the Senate on May 16, 2023 to amend Title 28 to add four seats (12 associate + 1 chief = 13 justices). Confirmed via govinfo.gov (sponsor Edward J. Markey; 'allow for 12 associate justices'; introduced 5/16/2023, referred to Committee on the Judiciary) and his own Senate press release, which lists him as a lead sponsor and describes expanding the Court by four seats to a 13-justice bench. He led the reintroduction rollout publicly. The bill was read twice and referred to the Judiciary Committee and never advanced to a vote or became law (Congress.gov latest action), so it is not FULL/PARTIAL; but he actively led and drove the effort beyond a single supporting vote, which is exactly CHAMPIONED. The non-advancement reflects lack of a Senate majority for court expansion, not any retreat by Markey. Same standard would yield CHAMPIONED for a sponsor of either party who introduced and led a signature bill that died in committee. Prior rating's sources are real and support the outcome; Congress.gov and LegiScan block automated fetch (HTTP 403) but are the live canonical records and are corroborated by govinfo.gov, which I fetched successfully.