I have not seen any comments here that address a certain buyer motivation for concessions, lack of funds for closing costs. Everyone advocating for adjustments 100% of the time forgets that we only adjust when the market says so. That is why the concession adjustment is not necessarily dollar for dollar with the adjustment. I have found in many cases when there is a seller concession that the buyer and seller are fine with the sale price. The issue is the buyer lacks the funds to close. Therefore, when you ask the question, "would this property have sold for less if there was no concession?" the answer would have been "no". It just may have sold with a different buyer.
On the other hand, if seller concessions are rare, if it sells for higher than asking price (especially if the amount over asking price is equal to the concession) or if the concession is added after the "meeting of the minds" and the price changes then yes, it would have sold for less and you adjust. The key, as always, is explain, explain, explain your work.