Sorry Scott, but you're not entirely correct, so I suggest you watch it again. While that is what was said in the film, they were not a hundred per cent certain as to which cabin it was.
As I've already stated above, the cabin that they were exploring was on B deck; I clearly remember the MIR submersible going over the bow, since it was assumed that Margaret Brown had a cabin overlooking the bow. But this was incorrect; her cabin was on E deck. Plus, they filmed GOTA in 2001 and it wasn't public knowledge until a year later, when Daniel Klistorner's article was released that there was conflicting information. Besides, James Cameron did not get past D deck in GOTA.
I know Parks or Daniel will back me up on this. Plus, Daniel's article that I linked to above should be the last word on which cabin Margaret Brown stayed in.