Just to get started, 21H's are 1951 to 1958, 22H's are 1958 to 1963, 122/142/147/145's are late 1963 and later.
Additionally, some organs have been pieced together in order to get one working unit out of many; this will produce inconsistent and unlikely date code ranges.
Some of the entries on the age list show actual known production dates and can be used as markers to guage the quality of other entries around them.
Until this work is published, the Age List will continue to function more or less as it has; a quasi-definitive source of this information and a registry of Hammond and Leslie product owners.
Later Leslie motors have a sticker on them indicating their manufacturing date.
The formula is XXX-YYWW, where XXX is the manufacturer EIA code (190 indicates General Instrument in the present example), YY is the last two digits of the year of manufacture, and WW is the week of manufacture.
What follows is a breakdown of the more common parts and a description of their codes.