As close as I can tell, the 75 hp Mercury outboard, serial number 9436217 would have been manufactured in late 1985, since the 1986-on models, were six digit serial numbers with an "A" prefix.
you have a 55 hp 1980 model
A 9.9 hp Mercury outboard, serial number OB235459 is a 1988 model.
A 9.9hp Mercury outboard, serial number OB120743, is a 1987 year model.
A 35hp Mercury outboard, serial number A184641, 1985 year model.
A 9.9hp Mercury outboard, serial number OD127373, is a late 1992 year model.
A 20 hp Mercury outboard, serial number OG156340, is a 1995 year model.
Two items are required to determine the year model of a Mercury outboard, the serial number, and the horsepower rating.
A 175 hp Mercury outboard, serial number 5921200, would be a 1981 year model.
In addition to the serial number, the horsepower rating is required to determine the year model of a Mercury outboard.
An 8 hp Mercury outboard, serial number OD134137, is a 1992 year model.
A 35 hp Mercury outboard, serial number 1763352, would be a 1965 year model.
A 35hp Mercury outboard, serial number 6445947, would be a 1984 model.