One other point:
After hearing my story and talked to the hotel, the SPG rep told me a different story: the hotel only upgrades SPG platinum to Bienville suites, which is their junior suites. What I booked were suites with river views, which were not supposed to be given out to SPG platinum memebers. That's why they told me no suite available.
Some years ago, Lurker wrote a very informative explanation of the numerous reasons why "suites available online" is not equivalent to "suites available for Plat upgrade." (I wish I'd made a note of the link; can't find it now.) One of the factors was the rule that properties need only make their lowest-level suite available for such upgrades.