I've only done one Platinum cruise thusfar, but AFAIK, there are no Platinum behind the scenes tours any longer. DCL has been cutting back on most of the CC perks. Now, on a longer cruise, there may be a special event, but it's not a regular offering.
I know you can go to Guest Services once onboard to inquire about a galley tour. But that's available to everyone, if they do it. It's not a given.
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