Magic Chef Furance age

Inspection this AM turned up a Magic Chef furnace. Condo built in 1980, thinking furnace is same age and in very good shape. Please help determine age, as I couldn’t find anything in The Technical Reference guide from Carson Dunlop. Thanks in advance for your help!

Model: G6A75DC10-11

Serial: A18912JGB.

MAGIC CHEF**: **from 1984 through 1998 has serial numbers with one letter, five numbers, and then three letters.
Last three letters of the serial number are date and place of manufacture where the first letter is the month and the middle letter is the Year and the last letter is the place.

A = January B = February C = March D = April E = May F = June G = July H = August
I = September J = October L = November M = December

A = 1980 B = 1981 C = 1982 D = 1983………S = 1997 T = 1998……

October 1986

Thanks Jae, much appreciated.

The letter “I” is not used, so its actually September 1986.