"It would be interesting to know who first commented on 'blue notes,' however they might have been described, and when. The Oxford English dictionary's earliest example of the sense we mean is from so late as 1915" "'Blue' Note melody" appears on p. 2 of the 1913 edition of "Memphis Blues" (whose copy Handy had nothing to do with).

"Earlier than that it simply meant 'an incorrect or off-pitch note.'" What's your source for that?