This assumes a world where Twitter (or a Twitter like) company would have moved into what was an effectively abandoned building. They didn't displace $40M of tax revenue that would have been there and it's unlikely that they would have moved there. Now that neighborhood has a market, a coffee shop, several restaurants and a bar (all paying taxes that likely wouldn't have existed).

It seems like the city got more than they were hoping for. The neighborhood is improved, safer and no one was displaced. Square and Uber are next door and aren't getting any tax breaks (they moved into the old bank of america building which wasn't eligible for any of the tax breaks). The taxes from those two new companies along with the restaurants, shops, etc don't seem to be reflected in the (what seems to be) completely made up $40 M number.