Look at that thread again. It all (first to last post) dates from 2007!

And look at the last post of that thread: It says: It's not supposed to work, but it sometimes has. In other words, it sounds like maybe it never reduced your rate at the reservation, but sometimes (but not guaranteed) it ended up with you not charged for the third night?

In other words, this doesn't sound like a code you should use if you don't want to pay the regular room rate. This sounds like a code you could use if you can't find anything better, and you want to "experiment" with whether you'll get charged less or not.

(Me, personally, I don't like such experiments. I'd look for a lower confirmable rate, like the normal $89 you mentioned, and ignore such an iffy discount code. But maybe that's just me...)

FWIW, I've found (in various hotel programs, not just Marriott) many discount codes that produce no discount from the lowest rate in an area. Sometimes they produce a discount only at the most expensive hotels (and then only a slight discount, so if I was looking for the least expensive hotel, who cares), sometimes they produce a discount only for certain room types (not the cheapest room type at the hotel), sometimes they add "more" to your room rather than lowering the cost (but whether that "more" is of any use to your not, that's a separate question). And some raise the price you see at first glance on a hotel because either they only work for some room types (and not the cheapest, and now it's only showing you the room types the rate works with), or because they add "more" but then charge a substaintial part of the cost of that "more" (ie, a rate might give you breakfast for two people at slightly below the in-hotel cost of the breakfast for two people, but way above the in-hotel cost of the breakfast for one person).