ok, and what is _office_? 

we don't have definition in OSM wiki https://wiki.openstreetmap.org/wiki/Key:office

so let's read wikipedia https://en.wikipedia.org/wiki/Office

"An office is also an architectural and design phenomenon, including small offices, such as a bench in the corner of a small business or a room in someone's home (see small office/home office), entire floors of buildings, and **massive buildings dedicated entirely to one company**."

so complex of several massive buildings may be called office


