For clarification, these results mean the problems are difficult when some aspect of the problem size grows (e.g. dictionary size, alphabet size, ...). For example for letter boxed, the size of the square can vary, so can the alphabet size and dictionary of words. See Table 1.

It is not really meaningful to talk about the computational complexity of most problems exactly as they are published in NYT, or they end up trivially in P, since the problem description length is bounded by finite English letters, fixed board size, finite English dictionary etc.