James Cameron did in 2001 according to Ken M. try to explore lots of areas of the stern, for example the Turbine room but Jake and Elwood where too big. The 2005 Bots probably could have gotten into most areas of the stern But Jim assumed it would have collapsed so much by 05 that there would be nothing worthwhile to see.
On Parks site Ken talks about this in depth but from the lights of the Mir 1 & 2 they did think they did see some paint on it still and other intact structures inside the ship through portholes