For example, on the photo below this guitar is without doubt a H22 (You can type a model number, with the H, on the search box on top of this page).
Remember that all Harmony made guitars (this means all guitars on this website) are still considered low grade instruments by most players and collectors, and can't be compared in value to the "great" names as Gibson, Fender, Martin...
As a result, only a handful of guys in the world are ready to pay real money for a rare Harmony model.
These are supposedly the manufacture date of the electrical harness or pickguard assembly, by Rowe Industries, but should give a close guess to the year of production of the guitar itself.
- I have a Harmony Rocket that is labeled as a H56. All pictures that we have seen have identified it as a H54.
Either they re-used a back prepared for the previous batch, two years before on the line, or they mistakenly used a 1961 stamp in 1963.