I can’t seem to get Date added or Last played date to work in Smart Playlists and Smart Filters.

I have an Active playlist that specifies:
Keyword hierarchy: Album/Series
Smart Filter: Play Count is 0.

Now and then I add something that we never get around to watching. Eventually, so it doesn’t clutter up the list forever, I just manually set the play count to 1. However, this makes it a bit problematic to review things we never watched to see if we just didn’t get to them, or if we really don’t want them. So I tried two things, neither of which worked.

The first thing I thought was that, instead of setting the Play Count, I could use a cutoff date (which I would have to change periodically) on my playlist for new items:

Match all of the following rules:
Play Count is 0
Date Added is greater than 2015-01-01

but that did nothing; files added in 2014 are still shown.

Then I thought, OK, I’ll stick with marking the files as played; they are still identifiable because their Last played date field is empty. So I made a Smart Playlist:

Match all of the following rules:
Play Count is not 0
Last played date is (left empty)

That showed nothing. In fact, everything I’ve tried in the Last played date condition, such as:

Last played date is less than 2010-01-01
Last played date is greater than 2016-01-01
Last played date is less than 2015-03-19
Last played date is greater than 2015-03-19

has either shown everything with a non-zero Play Count (the greater than ones) or nothing at all (the less than ones).

How can these fields be used? In particular, how can I define a playlist that will identify everything in the database that has a non-zero Play Count but an empty Last played date field?