I've seen it mentioned somewhere (Wikipedia, perhaps?), and someone e-mailed asking the same question, but there doesn't seem to be any basis for the assertion that a different edition was published.
It's not impossible that the book was altered in some way, but it would be a pretty big deal if anything was added to it, so surely it would be be shouted about, not slipped out on the quiet?
I think that someone somewhere got a bit ahead of themselves: there
was a collector's series of books made available on subscription and by mail order in France, which added extra "making of"-type material to
some of the albums, similar to the stuff in Michael Farr's
The Complete Companion.
Someone
might have assumed that
Alph-Art was to be included, but it wasn't in that series, at least not when I last looked*.
It's entirely possible that one will come out – we've had the two versions so far, and Bernard Tordeur of the Hergé Archive has said in the past (
at Greenwich) that even by the time the second one had been prepared for publication, they had found further material which
might be added to a third version one day. Mind you, that was back in 2004!
So keep your fingers crossed, but don't hold your breath!
*
Update: It
was added to the series eventually.