The Stevens Mdl 77 began producton in 1954 thru 1971. Serial numbers were not required by Federal law on rifles and shotguns until the 1968 Gun Control Act. Before i had that HORRIBLE boating accident where all of my guns went down, I had about 2 dozen rifles and shotguns that never wore a serial number. Perfectly legal, they get entered in your record books as NSN. If you specimen HAD been military issue, it WOULD have a serial number- military required SNs on all guns they bought-
What we have here is... failure- to communicate.