[This tip doesn't save much time, but it's a reminder that iTunes is one of the last "power user" apps in the Apple consumer catalog.]
Starting in 2009 I began having problems with smart playlists. Sort order in iTunes wasn't being respected on the iPhone, playlists metadata didn't update correctly, and the last played and play count attributes weren't behaving as expected.
The problems seemed to vary over time, but podcasts were always a problem. Since I'm a huge In Our Time fan I felt this more than many.
Eventually I resigned myself to the bugs. Few people use iTunes' astoundingly well done smart playlists; they're a power user feature. Fixing them was never going to be an Apple priority.
Looking back I also wonder if Apple quietly changed the definition of "last played" around 2009, so that it was set only when a tune was completely finished. For music this would make sense; but the last minute of most podcasts is taken up with closing music and the like. Since I skip that for the next podcast, I would never "complete" a 45 minute program.
Without a working last played attribute I had to manually manage the list of podcasts that went to my iPhone. This minor chore bugged me until it occurred to me that the wonderous Doug's Apple Scripts for iTunes site might have a script solution. They do - New Play Count v2.0 will script the last played setting.
In the midst of doing this, however, I realized that the current context menu for a tune includes "reset plays" and "mark as Played"/"Mark as Unplayed". It's not a new feature -- I found a 2006 Google reference on this. I just missed it.
So I set all the podcasts I'd listened to as "played"; I didn't need the AppleScript. I created a simple playlist that only included IOT programs that were unplayed. Now I let my podcasts run to the end, so I'm hoping I'll eliminate that little chore.