You can use sales either before after or during the effective date. There is no FNMA, USPAP, FHA or any other reputable entity that says otherwise.
Think about it. A pending sale of the home next door that is the same model as the subject shows $200,000 on MLS as of the effective date. It closes the next day for $150,000. You write the report and discover that this pending sold. This may be your best comp.
Why would you not use it?
Because some client decided that they don't like you to use a comp the day after the effective date?
Using it as a pending sale is misleading. Using it as a closed sale is solid and is a very powerful indicator of value. Make it comp 1 in all caps. Emphasize in the report that this is the best comp BECAUSE it closed the day after the effective date of the report. That is by far the most recent sale and the most proximate sale.
Comps dated before or after the effective date are supposed to be selected based on what the appraiser thinks is reasonable, NOT what the AMC thinks is reasonable.
The thinking that we cannot use comps that closed after the effective date is just like any other old wives tale. The rumor just keeps spreading, even though it is not true.