If you search online there are plenty of posts of people claiming to have found "unsolveable" parlour puzzles, and every one I've seen ends up being actually solveable and was simply a result of a rules misunderstanding or wrongful (or) missed assumption. For example: we must enter the Parlour Game with the assumption that the game can be solved. So we can always exclude any configurations of true/false that would lead to an unknowable end result. This is an assumption many miss. When boxes with multiple statements get introduced, there is also the fact that one box must have only true statements, and one must have only false statements. This is another one many miss that lead to wrongfully called "unsolveable" puzzles.