Every series episode is either checked or unchecked.
A checked episode has been watched.
Checkmarks are retained in the SeriesInfo Database, even after the physical recorded TV file is deleted. To access the SeriesInfo Database, install and run Recorded TV Manager 3 and select SeriesInfo... from the Tools menu.
If the AutoDelete option Automatically delete checked episodes is enabled, then any new recordings of checked episodes are deleted immediately after being recorded.
AutoCopy Rules
The AutoCopy OnDelete rule provides an action clause to "Check deleted episode". Whenever an episode is deleted, the episode is automatically checked. It's also possible to create an OnDelete rule which doesn't move anything, but just "checks" the episode.
Recorded TV Manager 3
Every episode has a checkmark associated with it.
Check or uncheck episodes with the mouse.
Changes in the checked status are automatically applied to the SeriesInfo Database.
SeriesInfo Database
Access the SeriesInfo Database using the Tools menu in Recorded TV Manager 3.
See SeriesInfo Database for more information on checked episodes and more options, including Check on Play.
Recorded TV Media Center Add-in
If you play a recording from either the Browse or Play Next page in the Media Center Add-in, the episode will be checked automatically depending on the setting of the Check on Play option for the series (see SeriesInfo Database).
You can also toggle the checkmark for an episode from the History page of the Media Center Add-in. Select an episode and then press OK to toggle the checkmark ON or OFF.