Thanks for the speedy reply. I should have mentioned that I had the tire inside out and ride side out while looking for sharps. I'm looking again, though. In case anyone things it matters, the tires are folding bead, panaracer T-Serv PT tires...

I studied the holes more closely on both tubes, and the holes are all on the 'inside' where the tube is more likely to be in contact with the rim. I'm taking a more careful look at the rim tape and the inside of the rim now, too.

Grrr!