Thanks all. The issue is resolved. I ultimately obtained a King Deluxe room for my free night certificate stays. This is reflected in the official reservations. Next time I'll pay more attention to Standard room types. Never expected this room type at an IC. But then again it's Tokyo where space is at a premium?
I'm tempted to cancel, however, given I had to be granted two room upgrades to receive a King bed. Then stay at the Prince Sakura Tokyo Tower. On the other hand, IC Strings has high ratings, a covered walkway to Shinagawa Station, and they finally came through. If I keep the reservation, I could save the Marriott points for a high tier Marriott or Ritz-Carlton some other trip.