This goes for all frozen foods: it is always recommended to check carefully for signs of spoilage once frozen and thawed and before consuming. In case of pecan pie, you can usually tell at a single glance if the pie can still be eaten or not. All the same, still check for the following signs. If it looks too mushy, smells off, chances are that it has gone bad. If you see growths of molds on the surface, it is a good idea to discard the pecan pie as it has likely gone bad.