I didn't get any responses, but I thought I would share with the community how I solved this problem.
It turns out that first, there is a bug in moodle that changes the maximum points for an assignment if it is edited. For example, the "Turn In Jewelry" assignment...If I edit it, the default changes to 100 points, instead of the 20 points I had initially assigned when I set up this assignment.
This bug, in turn causes the grades to not display for some items if a student achieved lower than the 50% minimum for a letter grade of an F.
To fix that problem, I had to create one more letter grade that accounted for all grades lower than 50%. It was also an F, but its bottom score was zero, instead of 50%. Once moodle knew what to do with lower than 50% grades, the letter grades started showing up in the gradebook.
Thought you all would like to know!