Hi Miguel, with reference to https://github.com/python/cpython/pull/25760#issuecomment-830338306, Guido rejected the PR because he said that the current docs are correct.

This is a major point of confusion for many people, but here's why a single feature can be added in 2 versions: PEP 484 (Type Hints) was initially accepted as 'Provisional' (you can see what this means in PEP 1). To spare you the details, it's a special pass for typing.py to add new features in point releases, and to backport new features to older versions - even if they aren't bugfixes! This goes against what most of CPython allows (new features usually aren't allowed to be backported). However, at the time, typing.py was pretty new, so there wasn't much existing code to break anyways.

Another example is asyncio. Which has since lost its provisional status a long time ago AFAIK. typing.py became de-facto non-provisional in 3.7, though PEP 484 hasn't been updated yet. This is why you may see stuff overlapping between 3.5 and 3.6.

I hope you learnt something cool :). Hope to see you around contributing to other parts of CPython!