Thanks again to everyone for the help. I did check the prior ticket number and it did, indeed, show the wrong date even on the UA site even though the confirmation number lookup reflected the right date. So near as I can tell, OZ was right, UA agent was wrong.

Getting the UA agent to reissue both made it all work. I waited 12+ hours, called OZ and they see everything as good to go (although, for some reason my seats have been changed so we're nowhere near each other -- we'll live being apart for a few hours!) I also called TK and AI and they both confirm all is good and even my seats+veg meal stayed intact.

Looks like I'm good to go, but I'll babysit the reservations. Again, my thanks for the help and the education.