The cycle repeats every 23 years, with 1957 being A, 1958 being B, and so on with all letters except I, O, and Q being used (so 1980 was A again).
The final letter of the serial number, which is a string of 11 letters and digits that denotes a year code, will be present.
It is extremely easy to determine the year of manufacturing for models made starting in 1957. As they are both a part of the same Hyster-Yale company, take note that this frequently holds true for Yale forklift models. The backup place for the serial number on a Hyster forklift is under the hood on the right side of the forklift.