As far as updating the PEP goes, it's a rare PEP indeed that is implemented
exactly according to spec - the integration process almost always uncovers
details that don't quite work out the way we thought they would.

For minor issues, we usually handle such changes without updating the PEP -
the issue tracker and the reference docs become the authoritative source.

Larger issues get discussed again on python-dev, and may lead to PEP
updates or even an additional PEP. That's pretty rare, though, as it
requires the original PEP discussion to miss something big.