This should do it assuming I understand your requirements, specifically that the R or N appears only when there is a matching tag.
Code:
program:
x=list_item(
list_intersection(
field("tag"),
"Tag 1,Tag 2, Tag 3",
","),
0,",");
test(x, strcat(field('#mybool'), ' - ', x), '')
Note that you don't need to explicitly create a list (your use of sublist). A string of SEPARATOR-separated values works.