^^That. The two 'dots' seen below the 'U.S.A.' are the indicator of vintage, in combination with the font/typeface used in the stamping. A 1970 stamp would show 10 dots, with one dot being removed with each following year. That leaves 2 dots in 1978 (and 1 dot in '79). Handles on that knife are delrin.
Late 1960s-vintage knives (1965-'69) had essentially the same/similar stamping, but without the dots below the 'U.S.A.' stamp. 1970 was the first year to use the dot dating convention.
1980s Case knives used the same 'dots' convention, but the font/typeface was changed to a more angular look (most recognizable by the so-called 'lightning S' in the CASE stamping, in that decade).
That's a GREAT find for $20. Nice score!
David