As Realtors we don't have reports that give us the difference in price between assessed value and sale price. We almost never use assessed value when pricing a home. We help our sellers determine an asking price. A buyer's agent helps the buyer determine a reasonable offer price and then the buyers and sellers agree on a sale price. All of this is done based on recent sales. There are a lot of factors that go into determining a sale price. All are specific to a particular home. The process the town uses to value a home is very different.
The real estate market changes rapidly and a two year period is a very long time. If we were able to provide this data, I would expect that it would not be very accurate for todays market. Many homes can be sold, resold, foreclosed upon, etc. creating duplicate information. Generalizing any results would prove to be inaccurate.