No one has ever published a method of discerning the manufacturing year of any Fed body based on the serial number that I am aware of. However, if you can be reasonably sure that the lens on the camera is the original one, the first two digits of the lens SN are supposed to indicate the year in the 20th Century when it was made. That could correspond to within a year or two of when the body itself was made. There could however be an exception with some of the later Induster 61 L/D lenses. I have two of them with staring didgits in the low 90's. I don't know if they were actually made that late, and it could be an erroneous assumtion for those models. There are also exceptions for some lenses with odd serial numbers because they may have been test models (similar to beta testing?) and bodies which may have been stored at the factory as parts and assembled many years later to convert inventory into cash. It's possible (even likely) that some late Fed-5 models were actually made in the Ukraine after the dissolution of the USSR, although I have actually heard of any being stamped, "Made in Ukraine".
-Paul
-Paul