Greece Cover - Why 2 Different Cancels?

Hi all,
I got this cover in an airmail lot. Looking at the cancels, I am a bit puzzled. I see 2 reasons:
1. Airmail had to have a cancel where it was put into the airmail
the Town/city could sometimes not be read if it was on the stamps.
So a habit was formed to cancel airmail away from the stamps and to invalidate the stamps with a 2nd canceller.
2. The stamps were cancelled on an island and on the mainland the dated cancel was added.
On the reverse there is only a pencil annotation: Posted on Kala Nera

Thank you for your answers!
Heinrich

Have no idea of the geography but I'd suggest it was mailed (surface) in MHAEAI and delivered to airport post office number 266 from where it was sent airmail to West Germany.

Hello Heinrich,

your cover was posted from the beach community of "Kala Nera" on the Pagasetic Gulf (you can easily trace in through Google maps). It was cancelled with the postmark of a rural carrier ("266" denotes the rural carrier route) and then at the closest post-office, that of Mileai - Milies