Great question - traditionally it was never included but now, many Realtors have started including the finished basement sq footage. A Realtor has easy access to public records and they will always be able to verify that information for any property. In this instance, it does not include the basement, however this property is already under contract.
It is in Foxcroft - if you are interested in this neighborhood, depending on your timeframe, I know another family who is looking to sell...maybe at the end of the school year.
Feel free to reach out 484 947 3127 - I work mainly in the areas covered by the Downingtown School district.
My blog has more information that might be valuable to you - http://downingtownrealestate.blogspot.com/