Bruce makes a very good point. There is no real way of knowing a S&W's birth date without getting a factory letter. They often stock piled parts to be used up at a much latter date. While the serial numbers are good clues it is not uncommon to see a gun born on a date long after that serial number block was used up.
For as many of these guns you buy the book would be a good investment for you. Really not all that expensive.