Duplicate matching
MythTV will, unless you tell it otherwise, try and not record programs that have already been recorded. There are four different methods it can use to determine if a program is a duplicate.
Subtitle
The scheduler will compare the subtitles of the new epsiode with any recorded(watched,unwatched or deleted) episode and if they match then it will not record the new showing.
Description
The scheduler will compare the description of the new epsiode with any recorded(watched,unwatched or deleted) episode and if they match exactly then it will not record the new showing.
Subtitle and Description
The scheduler will compare the subtitles and description of the new epsiode with any recorded(watched,unwatched or deleted) episode and if they both match exactly then it will not record the new showing.
Subtitle then Description
The scheduler will compare the subtitles of the new epsiode with any recorded(watched,unwatched or deleted) episode and if they match exactly then it will check the description and only if the descriptions are also identical then it will not record the new showing.