We then have a quite different situation from what raw SPF processing
would indicate. Thus I claim the rules deserve to be relaxed (without
going into detail how).
The point I was attempting to make is that SPF records _can_
accurately reflect sender policy, while SPF processing will
incorrectly indicate a violation of it.
That's quite correct. I say "quite" because SPF provides for various
levels of results, without mandating any particular behavior. However,
the quickest behavior, reject on fail, does not allow to examine the
message headers.