Imo, if the GSEs want supportive "proof" or evidence of adjustments, especially for market trends, then they should refine the MC form and make it so that every appraiser uses the MC form only because then at least teh program is consistent. All they need to do is break down the first six months into two quarters, and reuse TWO MC forms - one for the specific subject market of competing properties, which often is a far smaller data set, and another MC form for a relevant area market trend.
The way it is now, with different software offerings and a large difference among how appraisers select the data, can really skew results, both in trend and in other adjustments.