Joe,
Yes, the 2 or 3 digit number usually on the flat behind the recoil lug is an assembly number. It is also usually on the bott of the receiver and barrel plus on the TG & barrel band and sometimes on the BP. I don't believe that it is any help in dating the rifle. The serial number from the receiver should also be on the back of the bolt handle but if the bolt has been altered for a scope it is usually gone.
If the receiver markings are stippled out, then Sedgley put a number in the tang channel near the sear and also on the back of the bolt handle. I have yet to figure out any pattern of their numbers.
Dan