Basically, we can't know what work was done that warrented a crown stamp or crown/letter stamp. A plain crown stamp means the rifle was inspected, test fired and sighted in. A major repair would include the crown/letter stamp. If the barrel was replaced, the same stamp is placed on the barrel. Spare barrels manufactured in 1955 and later have the last digit of the bore diameter stamped close to the muzzle.
crown/C Carl Gustaf, Eskiltuna
crown/S Stockholms Tygstation, Stockholm
crown/K Karlsborg Tygstation, Karlsborg
crown/CB Karlsborg Tygstation, Karlsborg (Carlsborg, old spelling)