I’ve used this option for some time and it will only record new episodes and not the repeats that channels often broadcast throughout the week. Ideally, Virgin should make this the default recording option without users having to do this for every recording we set.
Access your planned recordings list (say recordings is fastest way) Find the series link in question and use the cursor to access the edit icon on the right (pen). Click on it and "New episodes only" is in the options list. This appears to need setting for every series link.