If you have copied/moved recordings to USB HDD beware.
The recordings list option 'programmes' lists all timers recorded both internal and USB HDD, indeed if you have copied off a single timer you will note the programme is now listed as 2 episodes, and no indication of where stored.
It is very easy to delete a programme in error thinking it is on the internal HDD when in fact it is has been archived off.
Suggestion:
If deleting programmes I would use the 'storage' option in the left pane and select either internal HDD or USB, you can be certain then that you are deleting the correct timer.