Replying to your post from a few days ago, but I wanted to make a small caveat for those who maybe don't spend much time on the cash side of things (in the same way from the other way around I know almost nothing about
DVC points booking), but Disney's hotel availability algorithms are generally heavily weighted to longer stays, and it especially doesn't like one night stays.
I agree with your results when searching one night, but if you tinker with date ranges enough you can find cash availability for many of the categories. Using all the Duo categories just for example, 12/31-1/1 no availability as you note, but 12/31-1/3 all three are available. Similar results can be seen for some of the other categories as well.
So since the search results are being influenced by Disney's algorithm preferences at that moment in time, it can make it hard to peg true occupancy/demand when it comes to single dates without doing several expanded date range searches around a point in time.
Hope that is helpful!