I think I have established by trial & reading the forum that editing commercials out of a recording is a hopeless task on the 9200.
Before the 9200 I would record to a DVD RAM disc, edit out the unwanted stuff & then dub machine to machine to get a finished disc.
Can anyone recommend a better method now I have the 9200?

Due to the way files are stored on the HDD, fine control of the cut-points is impossible, and the results are unpredictable.
Most users who need to do this transfer via USB to a PC (or faster via the IDE cable mod - which involves opening the PVR), but the PC edited file cannot be returned to the PVR HDD, only archived onto DVD or a media server/PC disc.
A slightly better top-and-tail edit can be had by playing back the file, and manually recording that, yes you can start and stop recording of the playing programme, but that runs at real time. If you separate the programme into ad sections, there is no way to re-join them, but you can select them in a playlist (selected files list) for consecutive playback.
The original recording can then be deleted.