I feel like you didn't read what I wrote😅 These are the districts I mentioned, they're a different split for a different reason. They're administrative regions, for governing purposes. I can't find an English link so apologies, but here's the wiki link for the geographical regions:

https://el.wikipedia.org/wiki/%CE%93%CE%B5%CF%89%CE%B3%CF%81%CE%B1%CF%86%CE%B9%CE%BA%CE%AC_%CE%B4%CE%B9%CE%B1%CE%BC%CE%B5%CF%81%CE%AF%CF%83%CE%BC%CE%B1%CF%84%CE%B1_%CF%84%CE%B7%CF%82_%CE%95%CE%BB%CE%BB%CE%AC%CE%B4%CE%B1%CF%82

Here's another link where both are mentioned in a schoolbook:

https://ebooks.edu.gr/ebooks/v/html/8547/2278/Geografia_E-Dimotikou_html-empl/indexC_34.html

We use the geographical split 99% of the time in every day speech, that's how we learnt the regions, the prefectures and their cities in geography in school. 

For example, no one uses "western Greece" when talking about regions in Greece, it's either Peloponnisos or Sterea Ellada. If someone mentions "Western Greece" in an everyday conversation they'd be talking about the general Western area of Greece, including the islands, not an official administrative area of Greece. To be honest I didn't even remember that part existed😅 

Also Thraki is always Thraki. That administrative region that's a combination is only used in political/government/relevant conversations.