14 white pawn captures, plus black a-pawn captured on a-file closes black balance. 15 white pieces on board, plus white bishop captured on c1 closes white balance.
Only last move by White to give Black a move on the previous turn is c5xb6. Piece captured must be black b-pawn as it couldn't have promoted. If Black's last was ...b7-b6+, then the position is dead as White must capture, giving stalemate. So last move had to be ...b7-b5 followed by c5xb6 en passant.
Previous 4 moves before that are also forced. Sb8xPa6 is illegal of course, in view of wPa7. Miguel Ambrona's deadpos program (enriched with his sherlock program) yields: ↶c5xb6ep ↶b7-b5 ↶Kb6-a5 ↶Kb4-c4 ↶Nb8-a6+ ↶Kc4-b4 1N6/PpPP4/1KPQR3/2PR4/B1kN4/8/1PPP4/8 b - - nsols 1
14 white pawn captures, plus black a-pawn captured on a-file closes black balance. 15 white pieces on board, plus white bishop captured on c1 closes white balance.
Only last move by White to give Black a move on the previous turn is c5xb6. Piece captured must be black b-pawn as it couldn't have promoted. If Black's last was ...b7-b6+, then the position is dead as White must capture, giving stalemate. So last move had to be ...b7-b5 followed by c5xb6 en passant.
Previous 4 moves before that are also forced. Sb8xPa6 is illegal of course, in view of wPa7. Miguel Ambrona's deadpos program (enriched with his sherlock program) yields: ↶c5xb6ep ↶b7-b5 ↶Kb6-a5 ↶Kb4-c4 ↶Nb8-a6+ ↶Kc4-b4 1N6/PpPP4/1KPQR3/2PR4/B1kN4/8/1PPP4/8 b - - nsols 1
