Hi Kim

The following wikipedia link shows a nice clear map of the national boundaries in the Balkans just before the First Balkan War in 1912:
https://upload.wikimedia.org/wikipe...kan_1912.svgGreece then held very less territory than today with much of northern Greece (with major towns such as Edessa, Salonica, Drama etc.) and the Aegean Islands all under Ottoman control.
These overprinted stamps were intended for use in newly acquired areas but after a time I believe they were used throughout Greece.
They were replaced in the newly Greek areas by the new Cross of Constantine and Eagle of Victory stamps.
Most of the other Greek overprints were intended for use in relatively limited areas.