Hamlet,
I really believe we are trying all very much too hard to parse a difference between "assumption" and extraordinary assumption" that is the incorrect difference here.
An "assumption," if later found to be false, should not alter the appraisers opinions and conclusions. An EA, if later found to be false, can alter the appraisers opinions and conclusions.
So an "assumption" that county data that says three bedrooms is correct, when that appraiser would not make any adjustements if the subject actually turned out to be a two or a four bedroom, would be an assumption that found later false did not alter the opinions of that appraiser.
An "assumption" that the county information the GLA is 1,800 is correct, only later it turns out the GLA is really 2,800 was not just an assumption, it was an extraordinary assumption. The fact it was false later affected the appraisers opinions and conclusions.
My opinion? The Fannie rep that said assuming GLA from a source believed to be correct, when it comes to GLA, to be ordinary and not extraordinary, when the typical standard for SFR mortgage work is to measure, and a seriously incorrect GLA DOES alter an appraisers opinions..... was someone that never understood the nature of an EA in the first place.
Webbed.