Thanks for thre report.  I overlooked 2.7 when updating the version switcher; the change will appear over the next 24 hours or so as the on-line docs get fully rebuilt.

> Also, 2.7 docs version switcher at the moment show `dev (3.9)` for 3.9 whereas the 3.8 docs say `3.9.0a0` can it be changed as well?

That's not quite accurate.  Only the 3.9 version of the documents show 3.9.0a0, not from any of the other versions; just as only the 3.8 version of the docs build shows 3.8.0 etc. That's an artifact of how the docs are built; we don't do anything to update the specific version.  Compare the version switchers for:

https://docs.python.org/3.7/
https://docs.python.org/3.8/
https://docs.python.org/3.9/

I don't that's worth trying to change.

> A PR (16848) has been opened now for the change for pre (3.8) to `3.8.0`.

No, it changes it to "3.8".  As noted above, only the 3.8 version of the docs when built will show the current 3.8.x release number.