Most content only stays available on iPlayer for 7 days after broadcast.
If a programme is repeated within that 7 day period, this might reset the 7 day availability window but this depends what rights the BBC have managed to aquire for that programme.
The BBC are allowed to series stack a small percentage of iPlayer content.
This means that episodes become available as they are broadcast and stay available until 7 days after the first broadcast of the final episode.
Repeats before the stack expires do NOT increase the availability time.
If a series stacked programme has more than 13 episodes, only the most recent 13 episodes will be available to watch again. Earlier episodes will dissapear as new ones are broadcast.