Following up on this - now that we're 18 months out from week 51 2022, my reservation appeared in the system as still in week 51 (12/17/22-12/24/22). I inquired in the vistana chatbox and received the following response: "Our Hawaii and Colorado properties offer Event Weeks 51 and 52, which cannot be confirmed using StarOptions, as Owners who own at these properties paid a higher premium to secure travel to their Home Resorts during these time-frames."
Thus, St John weeks 51/52 were NOT sold as event weeks and do not shift during 53-week years. Somewhat disappointing. If anyone has heard otherwise at WSJ, let me know.