I spotted this little handy tool: VMC DeDuper is a tool for removing duplicate recording entries from the schedule, it seems to scan through Recordings.xml and checks if any scheduled recordings have recorded already.

VMC Schedule DeDuper is a workaround for Media Center's propensity to record duplicate episodes of series. This hit me hard after moving all my recorded tv from one drive to another. Even though the episodes show up fine under Recorded TV, VMC still wanted to re-record about 50 episodes over the next two weeks.

You can download the binary and source code from HERE and get more info HERE

VMC Schedule DeDuper - Imadeagraph