if it was made before 1968 a serial number wasn't required
Center fire rifles were most defininetly required to be ser#'d before 1968 (GCA68).
It was only cal 22RF long guns and shotguns that were exempt from ser#ing by their manufacturers before.
All the GCA68 did was add those two catagorys of firearms (22RF cal long guns and shotguns) to the 'required to be ser#d' group.
With that addition,,then all (groups of firearms) were required to be ser#'d.
What happened at Marlin was the 22RF cal LeverMatics were being produced and were originally ser# when production started in the 50's.
Then later Marlin decided to stop ser#'g them as (both the 22rf and the 22Mag cal) rifles as cost saving thing. This was completely legal as this was pre 1968.
Center fire rifles were still required to be ser#'d however (pre 1968).
The Levermatic Model 62 ,the centerfire version of the rifle in 256 and 30Carbine, was introduced in 1963.
It should have been ser#'d /per Fed Law being a centerfire rifle.
But Marlin for some reason never thought to ser# the centerfire frames of the new Model 62 version when production began in '63.
They weren't ser#'g the rimfires at that point, so no one saw fit to set up a roll marking station to do the centerfire frames I guess. They all look the same,,, kinda.
They mfg'd and shipped a little over 4000 centerfire Levermatic Model 62 rifles out before anyone caught the problem.
This was still before 1968 and Marlin brought the 'issue' to the attention of the IRS (they had control of Fed Firearms Laws before the GCA68).
The slap on the hand to Marlin was to issue a continuing recall on all 4000+ Mod62 Levermatics mfg'd and sent out of the factory w/o a mfg applied ser#.
Those rifles returned to the factoiry by way of the recall,,or any such rifle that might come back to the Marlin factory for service would be issued a new IRS (Later BATF) approved ser# and such would be hand applied/stamped onto the left front side of the frame.
When I worked there in the Repair Dept in the early 70's we had a few come in but just by chance though repair requests. They got the ser# treatment.
Someone from the office would bring out the BATF paperwork and tell you what the ser# was to be wacked into it. Then record it in some manner in the paperwork. It was just a sequential number of course.
We tried to make it as neat as possible an application of the number, but being applied through the finish and then just left as-is, I doubt there were many happy customers upon the receipt of their rifle back from Repair.
A simple form letter somewhat explaining why the operation was done was included in with the rifle when returned.
That recall was supposed to be a forever thing,,but I don't know if it extended over to the Remington ownership era or not.
Anyway, that's the story of the centerfire rifle ser#'s before '68 and the Levermatics that escaped custody w/o one.
Many probably still on the loose doing damage to paper targets and woodchucks and such..