In their book, "Remington .22 Rimfire Rifles", John Gyde and Roy Marcot publish a chart that cross references serial number to approximate production date. They also explain that while this information is compiled from historical records at the Remington factory, there are a number of extenuating circumstances in Remingtons "system" that prevent a totally accurate date assignment. If you don't already have a copy of this book, I recommend that you add it to your library.
Best regards,