For what it's worth, my experience (use 'they') was (not that long, but) before then, in the UK.
What really irks me (as a result I suppose) is the sort of passive aggressive use of 'she' for gender unknown, as though righting some wrong or making some sort of point that we don't know it's 'he' either - true, that would be wrong too!
Matt Levine does it an awful lot, recently-ish I even noticed one was actually a man; he was just using it in the general sense not having checked who the specific person was in the role that he was talking about - 'they' would have been fine, but 'she' was more incorrect than usual, a factual error.