thomastonk: <Murky: Nimzowitsch was at his peak around the year 1927.> Nevertheless, in his comments he gave 12.. Ke7 as the reply to 12. Bxc7, and so he overlooked 13.c5! even after the game. ;-)
<12.Bxc7 is stronger than the played 12 Bh4.> Well, this was not clear to me and hence I have asked my silicon friends for advice.
Stockfish 1.9.1 prefers Bh4: +1.09 compared to +0.88 at depth 26.
Houdini 1.5 prefers Bh4 : +0.65 compared to +0.54 at depth 26.
Fritz 13 prefes Bh4: 1.48 compred to +1.25 at depth 25.
Critter 0.80 prefers Bxc7(!): +0.79 compared to +0.78 at depth 22.
Shredder 10 prefers Bh4: +1.04 compared to +0.71 at depth 20.
I have used similar computing times, which result in different depths.
A serious judgement would need more carefull inspection of the resulting positions and their possibilities, and hours of time, of course.