That isn't at all true. It was absolutely standard (British) English when I was growing up in the '80s.

Epicene they has been common all along. That's why curmudgeonly grammarians could never shut up about it--because it was so common. The recent innovation is the use of singular they in situations where gender would normally be assumed. For example, "Jane went to the restroom to comb their hair." Until recently that was jarring for most people--some more than others--even when they weren't invested in the culture wars.

TIL Usenet was in use in the 14th century.

What newsgroups did Chaucer post to?

Are you trying to claim that Chaucer used "they" as a gender neutral singular pronoun? That is extremely dubious considering that half of the Middle English speakers were still using <he> as the third person plural pronoun[1] (descended from Old English <híe> and unrelated to the third person masculine pronoun). Chaucer himself alternates between native Old English and Anglo-Norse forms depending on grammatical case and/or whim[2].

[1]: https://en.wiktionary.org/wiki/he#Middle_English-they [2]: https://sites.fas.harvard.edu/~chaucer/pronunciation/gr.html...

> The thing about singular they is that it only really became "perfectly good usage for longer than people think" within the last few years, well after the heyday of Usenet.

The singular "they" has been prescribed in manuals of style since the 1700s[0], continuously through the 20th century. That certainly predates the heyday of Usenet.

[0] https://en.wikipedia.org/wiki/He_(pronoun)#Gender