Common charges are estimated correctly unless it says otherwise in the offering plan. It's the Estimated Real Estate taxes you need to be concerned about. Does this building have a tax abatement already active or are they still waiting for an approval?
Sometimes when buildings do change CC charges depending on how many owners are living in the building, has anyone defaulted on their payments, does the building allow rentals (rent to own?), etc...
This is something you should discuss with your attorney to be absolutely sure. So while CC charges are accurate, they can change.
If you're determined to buy a condo right now, then it's much better to buy one in an established community. Those are much easier to value, but your mileage will vary.
Anyway, the common charges on new developments are estimates, and those estimates vary wildly. Also, those charges are subject to various market forces. Keep in mind that the costs for building materials is in constant flux. The fluctuating gas/oil prices, the titrating flow of credit, and overall sluggishness of the real-estate market aren't helping the situation. However, that doesn't mean one can't create new models that will generate more reasonable estimates for now. You'll simply have to sample the data periodically, and adjust your projections according to the amount of risk that you're willing to accept.