Billion has wildly different meanings. https://en.m.wikipedia.org/wiki/Billion
Removes any confusion for european and american collaboration.
Got old roots dating back to cockney trading slang: "The Old Lady just bought half a yard of cable"
The FT has a big international audience. As a German reader where a "Billion" is still 10^12 it does sometimes trip me up a little. So I at least find it useful.
Not trying to argue any point (I mean honestly...), just trying to understand the German POV here, which is interesting.
So the German reader will read the English article (in English, not auto-translated), see the word billion, think “oh that looks familiar” and might assume it means the same as the German word Billion.
Machine translation makes quite a few mistakes, so I think if you have some decent knowledge of a language, you might be better off reading the original rather than a machine translation. At least my point of view from a couple of years ago. But it's also possible that machine translation has gotten WAY better in the last couple of years, I'm not sure.
Anyone aged around 60 or older would have been learning these numbers before 1974, and that's a significant overlap with FT's audience. You are dismissing this as if it's Middle English. It's an entirely reasonable explanation, at least one that shouldn't be dismissed.
From the writing of the era, it's clear this new definition for million was not popular, and many chose to continue using the "British meaning." So it was probably in colloquial use for quite a while, and the transitional term "1 thousand million" became the proper style.
So there was confusion, even in the English-speaking world. Was. If I understand correctly, England has adopted 10^9, and so now there is no ambiguity.