Yes, that would explain most if not all of the 56-ply discrepancy. In the game on my page you can indeed see black making irreversible moves on move 50,100,150,

Yes, that would explain most if not all of the 56-ply discrepancy. In the game on my page you can indeed see black making irreversible moves on move 50,100,150, ... 450 and white's first irreversible moves comes only at move 500.