I can note two exceptions to;

"I maintain, though, that this isn't necessary nor always followed; that "white tie" on an invitation alone does not EXCLUDE the wearing of Highland Dress. I know of no exceptions to this."

The first is Nobel Prize awards.

The second is opening nights at the Vienna Opera.

Both events specify White Tie & Tails are the only accepted forms of attire.

I have attended both (obviously not as a recipient at the first) and can attest that any form of Highland attire would not be acceptable.