A couple of days ago I started a journey from Abbey Wood to Charing Cross - which I'd normally make entirely on National Rail. However, there was extensive disruption because of the weather - SouthEastern temporarily stopped running to Charing Cross - so accordingly I swapped to the DLR at Woolwich Arsenal, to complete the journey via Jubilee then Northern line. I assumed, that since I was now using National Rail AND TfL trains, I'd have to pay a much higher fare, but was pleasantly surprised when I checked my Oyster journey history to find I'd only been charged the National-Rail-only fare of £2.80. This despite that I exited Charing Cross from the underground barriers, so the system should have been able to tell that I had used the underground. I'm slightly curious as to on what basis the system would have charged me a national rail only fare? Does it only consider which stations you entered or exited at, and ignore whether you entered/exited via barriers that only lead to national rail, or only lead to the Underground? Or would there be some other reason why I was charged a national rail fare for that particular journey? Am I correct in assuming that I would have been charged more if I'd exited at any neighbouring station (such as Embankment)?