The Importance of Small Differences

Continuing with Lasker's Moves that Matter, the diagram shows a position that did *not* occur in the famous first game of the 1907 Marshall - Lasker World Championship match.

The diagram is the position after 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.d4 exd4 7.e5 Ne4 8.Nxd4 O-O 9.Nf5 d5 10.Bxc6 bxc6 11.Nxe7+ Qxe7. Soltis pointed out that it is similar to the Marshall - Lasker game, which opened 1.e4 e5 2.Nf3 Nc6 3.Bb5 Nf6 4.d4 exd4 5.O-O Be7 6.e5 Ne4 7.Nxd4 O-O 8.Nf5 d5 9.Bxc6 bxc6 10.Nxe7+ Qxe7. The only difference is the Pawn on a6, which was on a7 in the Lasker game.

(Not the)
World Championship Match (g.1)
New York 1907
Lasker, Emanuel

Marshall, Frank
(After 11.Qd8-e7(xN))
[FEN "r1b2rk1/2p1qppp/p1p5/3pP3/4n3/8/PPP2PPP/RNBQ1RK1 w - - 0 10"]

Soltis also mentioned that many annotators of the game assumed that White already had a bad game, although 'The position is nothing more than a transposition to a standard Lopez variation. The only difference is the addition of ...a6 to a position recognized today as just equal.'

Isn't the position of the Pawn on a6, which is on the same color as Black's remaining Bishop, the difference between an equal position and a a position which is slightly better for Black? The development Bc8-a6 is excluded in all variations. I have seen other positions where the advance of an a-Pawn or an h-Pawn from its second rank to its third is the difference between a good game and a not-so-good game. Perhaps the diagram is another example.