2021 January - Birdwatch launched with first 1000 users
2022 October - Elon acquires Twitter
2022 November - Birdwatch renamed to Community Notes
2022 December - Community Notes feature made available to tweets around the world
Maybe Elon pushed the release schedule timeline up, but it would not be correct to state that pre-Elon Twitter didn't develop and launch the feature. It had been live for almost 2 years by the time Musk showed up.
I was a fairly early Birdwatch tester; they definitely permitted political posts to be annotated. I can't recall either way on ads; given Musk never made a big "I'm enabling it on ads!" announcement I suspect it was always possible.
(Especially considering you can promote a post after the fact; it's not necessarily an ad to start with.)
When reddit first added fake/branded posts as ads for a short while it was possible for people to post on the branded posts. It was hilarious (vicious roasting of the products and brand) but of course that was quickly locked down.
2022 October - Elon acquires Twitter
2022 November - Birdwatch renamed to Community Notes
2022 December - Community Notes feature made available to tweets around the world
Maybe Elon pushed the release schedule timeline up, but it would not be correct to state that pre-Elon Twitter didn't develop and launch the feature. It had been live for almost 2 years by the time Musk showed up.