Returning, again, to the book Jerome Gambit, for another walk in the park (or in the weeds)...
A note given to the game "N,N"* - Blackburne, [London, 1885] brings much to mind.
The first eight moves of the game were 1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.Bxf7+ Kxf7 5.Nxe5+ Nxe5 6.Qh5+ g6 7.Qxe5 d6 8.Qxh8 Qxh4
9.d4
An improvement suggested by Munoz and Munoz in the August 1885 Brooklyn Chess Chronicle, repeated by Fletcher in Gambits Accepted (1954) and Druke in the November 1987 Gambit Revue, to give some early citations. (Actually, the move is rarely mentioned, but see "A Closer Look (Part V)".)
To add more, from the post "Update: Old Dog Can Still Bite",
White's Queen-escape line is, instead, 9.0-0 Nf6 10.Qd8 Bb6 11.e5 dxe5 12.Qd3.
This seems a lot saner than 9.d4, e.g. 9...Nf6 (or 9...Qxe4+) 10.e5 dxe5 11.Nd2 Bxd4 12.0-0 Be6!? when there is plenty of madness in the position after 13.Nf3 (or 13.Qxa8 Bd5 14.Qc8 Ng4 15.Qxc7+ [15.Nf3 Bxf3 16.Qxc7+ Kg8 17.Qc4+ Kf8 18.Bh6+ Qxh6 19.Qc8+ Ke7 20.Qc7+ etc] 15...Ke8 16.Nf3 Bxf3 17.Bf4 Bxf2+ 18.Kh1 Qh3 19.Qc8+ Ke7 20.Bg5+ Kf7 21.Qxg4 Qxg4 22.Rxf2 Qxg5 23.Rxf3+ Kg7 24.Re1) 13...Bxf2+ 14.Rxf2 Qxf2+ 15.Kxf2 Rxh8 16.Nxe5+. The game is even, if White survives.
All of this serves as a prelude to a piece of analysis from Jerome Gambit.
[9.d4! Nf6 10.e5 (10.dxc5? -0.80/20
10.e5 2.77 is much weaker Qxe4+
11.Be3 Qxg2 =/+ ) 10...dxe5 11.Nd2!
Repels Qe4 + (11.dxc5? 0.15/20
60
11.Nd2 2.46 looks very tantalising,
but Qe4+ 12.Be3 Qxg2-+ ) 11...Bxd4
12.0-0 +/- ]
[ with the idea 9.d4 1.87/23 Bb4+ 10.c3 ]
As the book assigns a "weighted error value" to each player's play in each game, it seems reasonable to assume that the author used Chessbase 16 in evaluations, as that is the first version where that number appeared.
Clearly, 9.d4 is the strongest move. In fact, Stockfish 16.1 (37 ply) assesses it as the only move that gives White an advantage.
The first game in The Database in which 9.d4 appears is Marfia - Stelter, offhand game, 1964 (1-0, 19) - almost 80 years after it was recommended. (Further research might find an earlier example.)
Arguably 9...Nf6 is Black's strongest response, although 9...Bb4+ comes into consideration, as does the energetic 9...Qxe4+ and the unsettling 9...Bh3.
Now (from "Jerome Gambit: Snappy Ending")
Capturing Black's Bishop with 10.dxc5 could lead to 19...Qxe4+ 11.Be3 Qxg2 12.Rf1 which is looked upon with disfavor by National Master Bruce Pandolfini in his Chess Openings: Traps & Zaps (1989).
The analysis from Jerome Gambit, above, indicates that 10.e5 is "much weaker" (due to [10.]Qxe4+ 11.Be3 Qxg2 =/+) but does not say much weaker than what?
I think the answer is 10.Nd2, recommended by Hindemburg Melao, in a 2003 internet article at www.superajedrez.com, in his notes to Amateur (Melao gave the name "Millner") - Blackburne, London, 188[5].
To date there are only 2 games with 10.Nd2 in The Database, one being perrypawnpusher - marvinni, Giuoco Piano Game, Chess.com, 2022 (1-0, 17).
Still, 10.e5 dxe5 is best followed by 11.Nd2, keeping the enemy Queen out of the e4 square (i.e. 11.dxc5? Qe4+ 12.Be3 Qxg2). Then 11...Bxd4 12.0-0 with an advantage to White - agreed.
*It was correct to simply write "NN", as this stands for "No Name", or Anonymous, or, in this particular case, as the player of the White pieces is also referred to, Amateur.
