If there are certain eras for the markings I do not know, However mine has a knurled receiver but the serial can still be made out, new serial in tang groove. The old serial is a low number! I have a Mann. carbine that was must likely stocked by Paul Jeager after he bought out Sedgley's stock of parts. Every part seems Sedgley except the stock. Barrel is marked with Sedgley name on the bottom and full original SA markings are still on receiver. New serial on 'rifle' is 988. 'Carbine' original number is 842988, strange!
You would probably have to do a survey to answer your question but that would still not give you a year but only a sequence.
You can never go home again.