I mentioned earlier, that all my TSU-reservations have the "STEX" acronym. I requested for a higher suite (new hotel, the HR Seragaki Island, Okinawa), and my concierge said it cannot be confirmed now, but depends on availability upon check-in. Concierge also stated, that my reservation "has a strong request" for an upgrade, and I now additionally have the "UPGR" acronym. I have updated the wiki with this additional acronym and my interpretation.