...assuming that Gail did indeed arrive. You might want to also check fairly carefully that liner strip covering the ends of the spokes hasn't worked its way off to the side somewhere around the rim, and that there aren't rough patches on the little strip where the rim got welded together (should be OK with anything but cheap rims, but never hurts to look), or for any dings on the inside of the rim if you have ever used metal rather than plastic aids in removing/replacing the tire from the rim. And any time you fix a flat, if you mark the relative orientation of tube and tire when you start removal, when you find where the hole is in the tube, it really localizes the area to look for on the tire. If the tire doesn't bet spun around on the rim when you do the repair, if the hole is in a different location from the prior flat, it is probably a good indication that it isn't just the same piece of debris still in the tire and not found the previous time, but something new. Flats aren't always really the fault of the tire, though lighter weight tires do tend to be a bit more vulnerable....
You're right, 5 out of 6 for sure.
First flat, 2 to 3 weeks ago, I think I followed most of your advice, except one, not marking tire position relative to tube. I did check the liner strip. I do use plastic gizmos to get the tire off/on. Once I got the tube off I put it in the sink to find the hole, saw that it was 13" from the valve and oriented to be the part most in contact with the road. All the while the tire was still loosely on the rim. So I felt all around the inside of the tire, and a little more carefully in the areas 13" from the valve stem hole, under the assumption that the tire hadn't rotated too much. Felt nothing sharp.
The guy at the bike shop said he had found a very small piece of metal imbedded in the tire, thought it was the culprit. I guess I should have also pulled the tire completely off the rim to have a better look at the inside, instead of just feeling blindly, but I guess I was thinking I just need to make sure there was no tack or something similar that would do in the next tube. After I got the first couple of rides in, I thought I was all set. So quite the surprise yesterday.