UPDATE #4: After some asking on Matplus a few weeks ago, I found that my 42 was already beaten. But I have an ego. It feels so good to have come so close! Anyhow, here’s the “new” records.
The 43 Mates:
Pd2-1, Pf2-2, Ph2,1, Nc3-2, Nh4-2, Qd4-4, Kf7-6, Rg5-12, Be4-13
The 47 Mates:
Pa7-1, Pd7-1, Ph7-1, Ne8-2, Qf5-4, Nd8-8, Be5-13, Rc4-14
I always knew that three pawn promotions. I just couldn’t figure it out myself. The same goes for giving the queen more moves.
UPDATE #3: I found 42 without extra promotions. I made that useless knight useful with 2 mates and I tacked on an extra discovered checkmate by giving the queen’s knight more freedom.
Slight Update: I found a way to keep the same result with one less pawn. I also moved the king to give the queen’s horse more room, even though it changes nothing. It’s just more elegant
The 42 Mates:
Rg2-14, Be5-13, Nc5-7 Ne8-2, Qb5-2, Ph7-1, Pa7-1, Pd3-1. Pe3-1
UPDATE #2-I’ve totally beaten that 36 with an astonishing 39! So darn close
to 40! Take a look! I shall heartily accept any flaws that you find!
If you could get 3 pawn promotion checkmates in a position that is similar to this, you could get 40, but due to the fragility of the set up, I severely doubt this. I was unable to do it myself.
The 39 Mates:
Pb7-1, Pd7-1, Pc2-1, Pe2-1, Bd4-13, Rf5-14, Ng4-6, Qh4-2
UPDATE: I have recently found a flaw Araud Mortier’s position. If the d4 bishop moves, then the black pawn can block the rook check. This also invalidated my answer as well. So I flipped the position for a new record of 36. This will no doubt be broken soon. This position is made for him.