Comps Used for Bank Appraisals vs. Reality

As the decline in the market continues to move forward, I am curious how bank appraisers will find appropriate comparable sales to value the property. Many of the closed transactions that they are looking at are based on contracts that were signed a year or two ago. It seems to me they (or Fannie or Freddie)could get burned by not taking this into consideration. It seems to me the last thing that they want to do lend money at the purchase price when the value has declined below that level. Do any bankers or brokers know if banks are becoming suspicious of the accuracy of comps on deals signed years ago or if their are too few recent comps to serve as a basis for valuation.