Well, I thought I would get some response from one of the developers, but I still spent a considerable amount of time researching and reading code. And while I have't found the answer from documentation, commentary or code inspection I think I can intuit from the patterns that the rawgrademax for the course final score is calculated by taking the category totals max points for all items that have been graded so far.
In this case the A students I mentioned in my original post had graded items in all categories except the Final Test category which has a category total of 30 points (out of 100). So 70 was used for the rawgrademax. When these students get graded for their final exam, the rawgrademax will then be adjusted to 100. So it appears the math is working that way.
I'm still not sure what caused the incorrect final score issue though, and I cannot duplicate that issue.
I'm still wondering though about question 5, How do I cause Moodle to recalculate grades without changing some values or overriding some values somewhere? If anyone knows of an easter egg somewhere that allows grades to be recalculated I'd like to know where that is.