1. Marisa, keep the pic. It's so summery, we need it around for the next three-four months, at least. (Need to do something about mine, too.)
2. Hi, Spiro. I'd keep this simple:
a. Κεντρικά γραφεία
b. Γραφεία διοίκησης
c. Γραφείο Ευρώπης
These are terms used by Greek companies, and they're not less descriptive than the English ones, probably more so.
Now, if anyone can tell me the difference between corporate office and corporate administration as the names of different sites, I'll tell you the difference between κεντρικά γραφεία and γραφεία διοίκησης.