Re: Gates' problem
Charles 9> and any source you cite will be guaranteed to be denied by someone else,
Given the 1st half-dozen Google.co.uk search returns all came back agreeing, I didn't think it needed citations. I did double-check in my trusty copy of The Economist Style Guide just in case there was some creative writing reason. But nah. that agreed too: Apostrophe before, not after decades. And not for plurals either.
But then I'm not an arts & humanities graduate and only went to a state school. So virtually self taught on the language side. So what do I know. I'll leave it to the experts.