And then it isn't.
The antiphon 'Vide, Domine" from Lauds of Holy Thursday was in the old breviary on another day during Holy Week.(Tuesday) So I don't have to set it myself!
I would need access to an antiphonale, not just a vesperale, so that I can find it. There are lots of Antiphonals on the internet, but because of the large volume such a document would inevitably have, many of them do not load correctly or load with missing pages or page errors. The last I tried (The antiphonal for the day hours according to the Dominican rite) had a file error and stopped after page 2. Luckily, I have one sure source: The hours from the Sarum Office that I get from This Site. I'll try it and see what happens.