I bet some of you were wondering if I miscounted again, but nope--apparently this is Arthur Conan Doyle's last collection of Sherlock Holmes. The very last--complete with the "I mean it this time" from the author. Hell, I'll let him tell it in his own words:
Well, looks like our duo's at it again, though the timeline varies between our gents being relatively young or much older and "retired." I have to say, though, for short stories, I couldn't stop until I'd read them all, and ended up doing so in one day.