For clarification, I was commenting on a few things:

1) It is possible that The Hotel Collection rate books via Seibu Global Rewards, which is a potential reason why OP couldn't see the booking through Marriott channels.

2) This hotel is an outlier in the sense that one can book through either Seibu Global Rewards or Marriott Bonvoy. Off the top of my head, I can't think of another hotel where I've stayed where that's possible outside of some casino resorts, such as Resorts World in Las Vegas, New York, and Bimini, which are affiliated with Hilton, Hyatt, and Hilton, respectively. There's also the case of Atlantis Paradise Island and Caesars but also has the ability to be booked through Marriott. I'm sure there are others, but I haven't stayed at another hotel that I know of that is affiliated with two hotel loyalty programs.

3) The multiple hotel loyalty programs with different benefits created confusion, since you pointed out in a previous post about how Marriott Platinum members and above get lounge access, but only SGR Diamond members get lounge access. In contrast, SGR Platinum and Diamond members get breakfast in the restaurant. This confusion caused Mrs. Majuki and me to be led to the restaurant during our first morning there, only to have the lounge attendant notify us of the mistake while we were halfway through our meal, which I described here.