If it's airing again in the 16 day guide, we have to find it there to mark it.
If it's not airing again in the 16 day guide, we have to use the curl method.
If it's a Pluto recording, we always have to use the curl method.
Please add Mark as not recorded to the DVR > Manage recordings and Library where it really belongs and is most useful.
The info needed (programID) is already there in the recording metadata (/dvr/files).