> Is PEP the best place for such updates? Maybe we can add a `versionchanged` note in https://docs.python.org/3/reference/simple_stmts.html#annotated-assignment-statements instead?

We should definitely update the docs, with `versionchanged`.

But we should also update the PEP, because the reason this was changed was an interpretation issue in the PEP.  This is different from simply changing things in a later version because we've come up with a new idea or we've learned that something was a bad idea.

Now that the intention of the PEP has been clarified, the PEP itself ought to be updated with words expressing the clearer version; but because previously the intended syntax wasn't supported, it makes sense to also add a note there that this wasn't implemented correctly until 3.8.