The first part of the serial number has no precise meaning relative to the date of production.It seems Harmony reset these numbers in every batch of the model, so a "6690H22" can be older than a "123H22" for example.- I have a Harmony Rocket that is labeled as a H56. All pictures that we have seen have identified it as a H54.Its very weird and I'm wondering if there was ever any rumors of misprints in the serial numbers. - Yes, it's definitely not rare to see "misprints" serial stamps inside Harmony guitars, between similar models.They were made on the same assembly line at the factory, and of course the body was the same before routing the holes.Misprints are especially common for popular models, as the Rocket electrics (H53/H54/H56/H59), or the Archtone acouctic archtops (H1213/H1214/H1215).As they were building similar models on the same line at the same time, we often see this kind of glitches between the model and the stamped number.
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).
As a result, only a handful of guys in the world are ready to pay real money for a rare Harmony model.
In the Harmony world, the interested buyer is often rarer than the guitar itself.
It looks like Harmony serial and date stamps were meant to manage the different parts and instruments on the production line, not to be used as reference by collectors 50 years later... - My brother has a Harmony Meteor in great shape but the the serial number is 84H8448. Do you think someone added the Meteor Label on the Headstock? - These stamped numbers inside Harmony made guitars were not intended as real serial numbers.
From what I have gathered on your site this indicates that it is an Airline. They were used to keep together various parts of the same guitar on the assembly line.