In the long and somewhat tangled Chess Publishing Forum thread on our Stonewall book, there is a question about move-orders in the 2.Nc3 line: How should Black react to 1.d4 f5 2.Nc3 Nf6 3.Bg5 d5 4.e3!? (Dia), planning a delayed capture on f6 and possibly saving a tempo by keeping the bishop on f1 (planning to meet ...Na6 with Bf1xa6 rather than Bd3xa6).
This is TalJechin's main suggestion. As far as I can see (I am having some minor problems with my ChessBase installation) the move is untested. It indeed makes some sense as the queen quite often goes to f3 in the 4.Bxf6 lines. However, the queen move isn't highly evaluated by Rybka and seems to fail achieving anything for quite concrete reasons (given below).
Other tries are:
a) After 5.Bd3 Na6, 6.Bxf6 or 6.Bxa6, probably transposing to lines covered in the book appears best as 6.Qf3 Ne4! looks strong.
b) 5.h3 looks very slow. However, after 5...Na6 6.Bxa6 actually gains a tempo over some lines where White plays Bf1-d3xa6, so Black may prefer 5...Qa5!?, hoping to use the ...Ba3 trick suggested elsewhere in the book after 6.Bxf6 exf6.
c) Other moves like 5.Nf3, 5.Nh3, or 5.Qd2 are certainly possible but I fail to see any clear idea behind them.
I am not convinced that 5...Qa5!? 6.Bxf6 exf6 7.O-O-O b5!? 8.Bxb5!? is quite as strong as Rybka thinks it is. But why go deeply into lines like that when the active knight move looks so simple and strong?
After 6.h4, 6...Qb6 looks stronger than the immediate capture on c3.
Also 6...dxe4 7.Qh3 Qa5+ 8.c3 Be6, planning ...Bf7 and ...h6 looks OK.
7.Qg3 Qa5+ 8.c3 Bf5 (Dia)
The position is quite interesting but I think it's already possible to conclude that Black is fine as he has more space and is not behind in development.
So, is this an omission?
Yes, probably it is. Foreseeing that a reader would be curious about the untested 5.Qf3 and related lines would have been quite difficult. But there should at least have been a sentence saying something like 'After 4.e3 c6, White probably has nothing better than 5.Bxf6, transposing back to our main line'.