Hope this is correct protocol to add my experience.
I use mail-merge to print ham radio certificates, and originally
imported a
tab-delimited .txt file, and the commas in the score were printed.
But I
found that mal-merge would simply stop printing after several hundred
when I used the tab-delimited file, so I imported that file into
excel,
and found all 2000 certificates were printed with no glitch, but then
discovered that, even though the comma is displayed in excel,
it is not printed by mail merge. So, I dropped back, use the
tab-delimited .txt file, and print 100 at a time and all is well,
no hangs, and the scores have commas.