Since most are in house and done by non-appraisers, I'd say very few. I do recall many moon ago, some aggressive appraisers who were doing reviews were turning in the appraisers they were reviewing. The investigator then required the review be sent in as well. Sometimes both the reviewer and the appraiser got to stand before the board and take their medicine. It got so bad the state director had to editorialize in the newsletter to reviewers to review their own work. So how many Std 3 reviews are really USPAP compliant? Who reviews the reviewer? I think George and Joyce are having a little problem wrapping their head around the issue that most states exempt bank employees from USPAP regulation. And non-mandatory states don't have to exempt them.
When I first started the reviews that were Std 3 compliant were either large complex properties or were a requirement of FHA who wanted a review of newbie appraisers. The rest were administrative in nature and done in house by the loan officer or a designated in house appraiser.
One of my former clients used to review our poultry farm appraisals one and all, but mostly by their CGs in house. But if overloaded they used to review them with outside appraisers who did do a full Std 3 review. Also, on FmHA backed farm loans, FmHA would review them in house and I've answered questions in both AR and OK. But again, they were professional appraisers used to correct errors in reports, rather than just resort to playing "gotcha".