Greece - Thrace Overprint - Type&value?

Hi, this Greek stamp is a mystery to me. A bit of digging taught me the overprint says 'management west Trace'. It further seems engraved because it is perf 13,5 x 13,5 (sorry if this is wrong reasoning, I am not an expert). Any clue on the specific type, and corresponding value?

Michel GR-TH OC9, Yvert GR-TH-63.
As you write Western Thrace (1920)

https://www.ebay.co.uk/itm/GREEK-OC...AOSw8DNftwW6

Greetings.

Welcome to Stamp Community Forum. Thank you for the clear message title, which encourages other Forum members to respond to your posting/question.

There isn't a relationship between printing method and perforation. Although knowing a Stamp's
perforation "size" can help distinguish between multiple catalogue entries.

The Scott postage stamp and the Stanley Gibbons catalogue each feature good discussions of
printing processes at the front of the respective catalogue.

It's relatively easy to determine if a stamp is engraved by running the pad of your finger across
the front face. You will (should) feel the raised ink. By contrast, lithographic and photograuve stamps will have a a smooth front face.

Note:
Your stamp is not perforated, it is "Serrate Rouletted"