Ooooh, I'm good!

Two years researching this now, and I have just found another date on the tour!

According to WC's interview with Jonas the band played a gig with The Police in one of the mid-west states and at last I have tied it down. Two sites list a Police gig at Glinnell University (outside Des Moines) in IOWA on 10th March, and one of those has those magic words "with Ultravox" beside the entry.
Hurrah!
Cross referencing this with the other tour dates when the two bands were in the US at the same time, it has to be this one.
Using my little map that I have put together this also ties in perfectly because obviously IA is en route across the country, giving the band 3 days before their appearance in San Francisco.
And as I have now also found out where the University of California is (Davis, CA) where JF and BC were interviewed, it is reasonably safe to assume that they, like the Police a few days later, played a set in the Coffee House This is in fact referred to in the interview. Davis is near Sacramento, a100km or so from SF so maybe this was the next day, after the SF gig? Certainly the next known gig was in LA two days later than SF.

I've now established 13 dates.
The definitive archive.

Buuut - they are FIVE DAYS between the gigs in Washington and Boston. That seems too long without a show. So maybe there is another one between 25 Feb and 3rd March?