I'm assuming we're talking NGOs here, because if we expand "organization" to include for-profit entities, then I'd argue vast majority of them will not just be US-English speaking, but US-originating and US-headquatered.

> Without such a conscious choice, yes, Americanisms do seem a fair bit more globally pervasive and easy to fall into "by accident".

You'd need choice and enforcement - unless such organization is testing for Received Pronunciation during interviews and filtering out people who cannot into Queen's English[0], I'd wager most of the members in such org, who don't come from UK (or a few related countries), will be speaking "British English" with distinctly US pronunciation. Because while an organization can make a conscious choice here, for most people, learning a second language is a long-term endeavor that largely happens "in the background", and it's very easy to learn a blend, with UK English being present in schools, and US English everywhere else.

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[0] - Or is it King's English now?

Coming from the horse's mouth, my expectation is that GP works at some kind of (non-military?) treaty organization? ime while outsiders might include NGOs under the umbrella, the kind of people who work at the "international level" tend to uhhh, care about their taxonomy. Multinational corporations are almost never lumped together with these (and generally don't really care about international cooperation as a goal, except instrumentally), outside the barest sense of "yeah, I guess they're organizations and they work internationally".

Majority counting by combined headcount of the organisation type maybe, but almost all multinationals are very big companies so by the law of "you get fewer number of pieces if each piece is large" there just aren't very many of them.