Ithaca Barrel Flat Stamps Question?

[Frank Good]

The older Ithacas such as my 1927 4ENID had the choke markings stamped on the barrel flats as seen in these photos. The "0"'s on each bbl as seen on the 24"bbl set are cylinder bore and the "4"'s on each bbl of the 30" set indicated full chokes and the factory letter indicated so as well. The 1957 Knick I recently purchased has a "3" stamped on the bbl flat and my 1926 Knick 5E has nothing of a choke type number stamp on it. Would the "3" seen in the pic on the '57 Knick be a choke mark or does it denote something else? Top pic is the Knick and bottom the NID