In Barney return the class reunion is 1948. In a earlier episode 3 years before the Class Reunion. They graduated in 1945.
Barney arrives in town in a 1958 Edsel Citation. When asked by Andy if it's a 1961 he says "no it's a 60 with a 61 bumper." That is incorrect. The bumper (as well as the entire front end) is, in fact, from a 1958 model. Also, Edsel was founded in 1957 it was decided to close the division in 1959. The last year of production was 1960. So there could not have been a 1961 bumper.