US here. I remember when it changed, probably 20-25 years ago. (Tho, of course it was gradual and localized and I’m only one data point.) I was an undergrad, and not in my first year.

IIRC, it was because “gulf stream” was a little ambiguous, because there’s a lot of gulfs many of which contain oceanic currents / stream. But, if someone in the U.S. or EU says “gulf stream” they are always talking about AMOC.