Having drafted architect's plans in a previous life, I can say that they do not measure the same way as ANSI- and even the AMS standard which differs from ANSI. But I've yet to see an assessor claim to measure by either AMS or ANSI. Architects measure by the stud walls sometimes, but by the sheathing at others. And the worst type of measure is by the center of the wall which, of course, is a hopeless form of measurement be you an appraiser or a builder. And depending upon the trusses, etc. They may have the sheathing flush with the foundation, especially when bricking.
Anyone trying to measure any of that within 0.1' is fooling only themselves.