Going back to the beginning (can be done here if you click on 'past posts'), you will find that the first edition was the first, and the second the second, and so on, all the way up to the fifth, which was the fourth (later rectified). But then the sixth was the sixth, so all was well for a while. Until the seventh was also the sixth.
But then, if you look at the first sixth, you'll see it wasn't an edition at all, so the seventh really was the sixth. Skipping ahead, the fifteenth was the fourteenth, and rightly so, but then, alas, so was the sixteenth (which no longer exists). However, the seventeenth was the sixteenth, so now all was then in order again. And has been ever since, actually.
Just checking. Nothing to see here. Move along.