In an Appraisal, every detail of the subject house is compared with the Comp houses:
If one has something the other house doesn't, an allowance in made to make them COMPARABLE.
You will hardly ever find two houses that are 100% the same, even in a cookie-cutter tract.
You have to trust that the Appraiser knew what he was doing.
Finding a similar house, within a short radius, was more important than finding one with a basement.
And there is almost always an allowance for the difference in SQFT
good luck, God bless and Happy Thanksgiving