I don't consider that review to be proof of an actual ST-release of Pool. The way it's worded doesn't necessarly imply the reviewer played it on an ST. I don't think people are lying either, but memories may be fuzzy.
If Pool was released (I wouldn't rule out that some version got leaked or something like that also) than it must be incredibly rare. As you correctly note, it's not in Planetemu's archive which is based on Tosec, and that's incomplete. But note: it's not on any known menu disk either. None of the proficent groups apparently released it which seems incredibly odd for such a game. Likewise I can say that there is no review of this version in the German magazines of that time (every other version was reviewed)
Furthermore the history of SSi games page found here:http://www.geocities.com/copeknight/index.html
considers it vaporware as well.
So personally, I believe it to be not released until somebody can produce some definitive proof (pics from an auction etc, or even better the actual game for the ST-community