"Greg Esres" wrote in message
...
Is it well-defined where the approach segment begins when you're
vectored for SHN NDB-A?

Yes, in theory. ;-) You're on the final approach segment where the
initial segment intersects the final approach course at (or within)
the 10 nm limit stated in the chart.

I see why it's a sensible practice to construe it that way, but is it
officially defined that way somewhere?

--Gary