Basements are generally calculated separately from the living space. The contributory value of basements is determined by the local market, government regulation, if it is finished or not (and the quality of the finish), and so on. (streetdirectory.com)

In the cost approach, all possible causes for the difference between the cost new of the improvements and the contributory value of the improvements at the time of appraisal must be analyzed. (Holland & Knight LLP)

Just because you didn't see a line item adjustment in the appraisal doesn't mean it wasn't considered. Every amenity attached to the actual real estate gets value, BUT it only gets contributory value not what you or the buyer/seller think its worth or what you paid for it. (ActiveRain Corp.)