I should have known better (no need for "I could have told you so's"). Louvre tickets book up early. I was looking four days early to buy Louvre tickets, and the only open slots were less than 2 hours before closing. Many days were completely sold out. Not a big deal for us, since we have been before and get the after-hours tour on our itinerary. Even if you buy the Paris Museum pass you still need to book a reserved entry time, subject to the same constraints. So, if you plan to visit the Louvre this summer on your own, I'd book at least a month in advance. Not sure I want to deal with capacity crowds, anyway.
We booked tickets for the Musee d'Orsay instead. There were many openings, even for the Manet/Degas exhibit running through July 23. I'd still book in advance for the Orsay, but you don't need to be quite so early.
