Nancy, I don't think Amex PTS discounts cruises on RSSC like some TA's, therefore the on-board extra credit (in addition to the $300 for Platinum holders booking through other lines) As I recall, you are charged the full brochure rate, then they give you that extra excursion credit. Someone correct me if I am wrong, please.

Only time I have ever used this Platinum service was for a hotel in Singapore prior to our one cruise with Silversea. The rate was better than I could find on the internet, and gave us a great room upgrade to waterfront, late check out, and (1) complimentary breakfast, even though there were 2 of us. (Joanna and I shared it)

Editing to say ( back the OP's comments!) I once or twice did not have my "letter" in the cabin for the $300 or $250(single occupancy) cabin credit from Amex. Just went down to reception early in the cruise, and they took care of it. I didn't e-mail Ngaire (hey, she might have been with me!), just told them the agency, and it was corrected by the afternoon