OK, I have started checking off "the list" of each csv file in both locations, and I found a few of them about 150 files into it that were not on either the asset list or the track project list. So, although during the first import of the assets the green indicator bar said "processing 1300 files", it in fact only brought in fewer, 38 fewer.
Why? Well, upon opening a few of the csv's in question, they did in fact have all zeros for depth values. Why is still a mystery, but they were converted from Dr. Depth. They were also not originally recorded by me, but by someone I share data with, but nevertheless, that's why they are not ending up in the project list. Mystery solved, at least concerning why they're not showing up in the project list. I won't worry about finding the other 25 or so, and assume they too have zero values.
So, bad CSV's to start. Garbage in, garbage out, or something like that! I will clean up the garbage, or fix it, and get on to the next task.