"Plus, it appears the appraiser might not have known if the plat of the subdivision was legally permissible when they got the number of lots wrong because it seems the subdivision was not approved at the time of the appraisal."
Absolutely right. The appraisal was developed as if it had been subdivided into 86 lot. If the property was not yet legally subdivided as of the valuation date, and was appraised on the basis that it was, then the appraisal was developed under an assumption that was false. This is a hypothetical condition; if it was not reported in the appraisal in compliance with USPAP HC standards, this would be a violation. Note: This would not be an extraordinary assumption if the effective date of the appraisal was prior to the subdivision approval date. An EA which assumes a condition in the future, like an EA that assumes completion of construction as of a certain is appropriate if the effective date is as of or subsequent to the assumed completion date. It is uncertain that will be the case, as of the effective date.
In this example, it sounds like a violation.
The underwriters would be justified in pointing out the violation and request the error be rectified with a revised appraisal as of the date of subdivision with the corrections required made throughout. This is an example of why there are USPAP Standards. Had the HC been documented properly I suspect the lender would have considered that acceptance of the reported value could change. Technically, no the appraisal is not "good". Perhaps the value difference is not significant enough to set off too many alarm bells, but this sounds like an error on the appraiser. Unless they did include the assumption properly. Then I'm a numb skull for the criticism.