to help make sense of the lettering is simple: if yours starts with CH9****
the "C" stands for chatsworth", which is where the original goose shop was in cali. If you had the "T" in front, it meant it was a higher model, (team or super) if you have no "T" its a motomag or standard version. the "H" in that serial is the 8th month, which is sept. And the "9" is the last digit of the year..1979. Sept 1979 mongoose.
some early serials start like this: CE9 or CD9...these 2 are may 1979 and april 1979.