From start of game to 50 squares left is enumerable.
From 36 moves left to end-of-game is apparently solvable.
The middle is the combinatorial explosion, and he avoids explaining how he navigates it.
A nitpick, but I don't think you meant to say "enumerable" here
"enumerable" means "able to be enumerated, or counted"
https://webstersdictionary1828.com/Dictionary/Enumerate
"innumerable" means "unable to be numbered, or counted"
The beginning and end of the game have less possibilities to consider. The midgame has the most possible moves = hardest to calculate.
If you read carefully, the midgame is the bit the author avoids explaining how to solve ;)