Cecil Moore wrote:
(snip)
The question is: For a well-designed coil, is the self-
resonance method valid for determining the delay through
a coil at HF frequencies below the self-resonant frequency?

Yes, that is an excellent question.

Since that's been an accepted way of doing it for more
than a century,

This is a conclusion I have not seen you support, except with repeated
assertions. Can you offer something more substantial? Surely a few
references have accumulated in that century. How did you learn about
this as the accepted way?

I don't see how anyone could object.

Man, what I don't see, could almost fill a universe.
But I don't use it to try to win arguments.