Hi Hilary,
I can get a list of AD group members into a repeating table/group (List-1B). My problem was that the checkbox I also placed in that repeating group was grayed out. So I was able to resolve that problem by creating a second repeating table/group (List-2B). I am using List-1B as my data source and I've added 25 default rows to my table.
If I set a default value on field-2b1 to "../../../my:List-1A/my:List-1B[count(current()/../preceding-sibling::my:List-2B) + 1]/my:field1b1" and I set the default value on field-2b2 to "../../../my:List-1A/my:List-1B/my:field-1b2[../my:field-1b1 = current()/../my:field-2b1]". My repeating table, List-2B will populate correctly. However, when I clear my fields and select another value from my DDL, the only rows that populate with data are the rows that remained empty after running my first query to AD.
I tried to use your filtering method to add the Set ID and Set Value rules on the Set field to assign values to fields field-2b1 and field-2b2 with the Set = 1 condition. However, I couldn't get my rows to populate.