@simontatham I wonder if some of this is a misunderstanding of the set of information you may be required to use to solve it. e.g I played a bit prompted by this toot, and ran into a game which had a corner like this.

Game is perfectly solvable, but only using the information that there are 170 mines on the board. You can't solve this corner with only local information, which surprised me.

(https://www.chiark.greenend.org.uk/~sgtatham/puzzles/js/mines.html#30x16:15,0,m63e3099956808ffbfa625e4c0b131198ba6da37aed14ffb3997c11081dfb2f16679f372561b93369f1db2f87bf1c442346633ed9763ca41436888873 if you're interested)