Does any one know how to date an Olympia Traveller produced after 1979?

The TWDB ends after 1979, see https://typewriterdatabase.com/olympia.61.typewriter-serial-number-database

On some Travellers there's a two digit number impressed in the frame, most likely a year. Carl H states it IS the production year and it fits the serial, see https://typewriterdatabase.com/1978-olympia-traveller-de-luxe.7764.typewriter and https://typewriterdatabase.com/1986-unis-tbm-de-luxe.8678.typewriter

However, I have a Traveller with serial 15-3846368 and the number 73. This serial fits in the year 1977. My theory is the number is the production year of the frame, not the typewriter.

So if there's no serial and only a number, we can only state the typewriter is produced AFTER the year represented by the number. As my Traveller demonstrates, it's not an accurate measurement for the production year of the typewriter (the frame was created 4 years earlier).

Any thoughts or information about this subject is greatly appreciated.