Update:
We are now down to 2 prefixes with exceptions.
One fixed 13 of 14 prefixes but seemingly missed one, so hopefully that will get fixed now that I've prodded them.
The other hasn't responded in a while. I emailed again and left a
voicemail. If I don't hear back, I'll probably just drop that one
if/when the other network fixes theirs. Then the exceptions will
be gone.
-- Richard