I get 1994 ... in your instance disregard the 1st two columns of the chart below.
1st row of info
20MSHS = Model#, where
20 = Horsepower
M = Manual tilt & start
S = 15" leg
H = Tiller
S = Year of manufacture in 1994
2nd row of info
Left = Model code
Middle digit = OB height
Right = Serial number
Does that '20MSHS' coding match what you have?