There's actually three options:
First Runs Only
First Runs & Reruns
All Episodes with duplicates
With the first 2 options Tivo should check the episode title and only record each episode once during a 28 day period (even if you delete it).
If you have the middle option and are still getting duplicates it could be because the guide data does not include full episode information. To workaround this setup a manual recording for one of the timeslots.
First Runs Only
First Runs & Reruns
All Episodes with duplicates
With the first 2 options Tivo should check the episode title and only record each episode once during a 28 day period (even if you delete it).
If you have the middle option and are still getting duplicates it could be because the guide data does not include full episode information. To workaround this setup a manual recording for one of the timeslots.