Bruce doesn't appear in truly physical difficulty at the end of TDK yet in TDKR he looks in pretty rough shape. That does argue that something else happened after TDK. For sure it doesn't make any sense that he'd been Batman for only a year before events in TDK.
If you use the time between BB and TDK (2005-2008) then he could have been operative for three years and then maybe another two mostly out of sight. And so the eight year period mentioned in TDKR is still supported by the last confirmed
sighting while he really ceased operations only six years before.
Seriously, though, that whole eight year absence is rather silly unless the last sighting isn't referring to the events of TDK and Batman remained operative for quite sometime after Dent's death.
Makes me wonder if anyone even bothered plotting this out at least on a piece of scrap paper to have it make more clear sense.