Probably you all know this but I just learned that Johnson and Langford boxed an exhibition in Boston on April 28 1906 at the Hub Theater.
Looks like you both need to buy Clay Moyle's biography on Langford which covers this exhibition bout.
This was two days after their actual fight.Years later Langford spun a lurid tale about how they went at it," hammer and tongs "during the exhibition and that it quickly turned into a real do or die fight.It didn't, newspaper reports say Johnson was," careful to avoid hitting Langford on his damaged eye that had been closed in their fight,"Boston Post , and that it was a pretty stately exhibition. To be fair to Sam he was probably trying to drum up interest in a rematch with the title on the line. As Beer Gut has said Clay Moyle has covered it in his excellent biography of Langford,which I highly recommend.
I bought it a few years back, then left it in Amsterdam airport, never got back round to purchasing it again.