Every maze here has exactly one route between the way in and the way out, with no loops and no squares closed off from the rest. That comes from how the maze is cut rather than from checking it afterwards, which is what lets the answer sheet be printed as the answer.
What makes a maze hard is the proportion of it that is wrong turns, not how big it is. Each page gives that figure for its own maze, counted rather than claimed.
They are cut by walking the grid at random and backing up at every dead end. It is the method that produces long corridors; the alternatives branch more often and give a maze that is solved at a glance.
A shaped maze is cut inside its silhouette rather than trimmed to it afterwards, so no corridor is left sliced open at the edge.