It's not bad math, I'm not saying that.
It's taken 19 weeks to get to 85% and 80% finalized of art and code (working on another 5% in both). That falls in line with your prediction. But it's still false expectations, assuming linear progress, without taking into consideration unforeseen circumstances, etc. You may end up being right; others have been correct before.
The point is though, a measurable number of people read unofficial estimations and begin to believe them. In the cases when reality does not match unofficial estimations, those people don't get mad at the player who posted the estimation - but they blame the developer for breaking promises.
That is one of the reasons why personal estimations should remain just that. Personal and private. For the greater good.
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