TiVo Community Forum Archive 1 (http://archive.tivocommunity.com/tivo-vb/index.php)
- TiVo Help Center (http://archive.tivocommunity.com/tivo-vb/forumdisplay.php?forumid=4)
-- Overwriting program logic & "First Runs" (http://archive.tivocommunity.com/tivo-vb/showthread.php?threadid=182550)

I'm pretty sure that the TiVo deletes programs in the order they expired. Which, if you haven't adjusted any save until dates, is the order they recorded.

TiVo used the Original Air Date [OAD] in a programs guide data to determine if a show is First Run. If the show airs within 28 days of the OAD it is considered first run.

However if there is generic guide data, such that the TiVo can't tell which episode is being aired, it will record as a first run show just to be safe.

Also there is a (IMHO) bug where movies that are also mini-series seem to always be treated as first run.

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Sony T-60 - 109 hours