Your example doesn't sound as bullet-proof to me as you think it does. Especially if you're using Pat to suggest that we don't know their gender.

I just looked at my messenger chat history for "they" and "their" and found all sorts of examples of where we use "their" in your example, like committing to "their repository" which sounds more natural in some cases when you're just talking about pseudonyms or when something is said so in-passing that you don't even bother to pin down a gender. These come so naturally that you don't even realize it, just like you aren't examining my use of singular-they in this comment.

I'd suggest something else: We vastly underestimate how often we use the singular "they/their". I've seen HNers rant against the use of the singular they only to find usage examples in their own post history from just a day before.

I don't underestimate it. I'm not a native English speaker and my native language has gendered nouns, verbs, and adjectives (and numbered adjectives).

This is wrong. A specific person of unknown gender was always they. “That person, right there: they are trespassing!”

It wasn't "always they." It's perhaps been more common in informal speech than formal writing until recently. But traditional usage would have been to use he if gender was unknown (unless it were assumed it was a woman for some reason).

Yup. The examples cited (at least a few years ago) all show a reference to a person from a group, never to a known individual. And it has never been common, except in fossilized expressions.

BTW, "Chaucer used it, so there" is pretty normative for a linguistic argument.

I agree. It's one thing to advocate for change to a language. Like the introduction of "Ms."

It's another to lie to justify your argument.