I'll have to get a magnifying glass. I haven't put the tire back on yet and I do have to go shopping. If I happen to see a magnifying glass, I'll check it today.

The only other possibility - other than an astounding set of coincidences - would be a previous hole damage wearing a hole in tubes. I've had that happen, but always with much bigger holes. Like I said, I have to really flex the tire a lot to even find the hole on the inside. Also, when this problem does happen, I expect to see rub marks around the hole, but I haven't seen any of that.