Last year I had the leg MAN->ATH->SKG->LCA (same booking ref) and LCA->ATH->MAN (another set of same booking ref). MAN -> ATH, SKG->LCA and ATH->MAN are successful to use coupons. However, the ticket in the leg of SKG->LCA and ATH->MAN cannot be issued. I need to ask the depature hall check-in counter in ATH and SKG to issue ATH->MAN and SKG->LCA respectively. It is not sure due to upgrade business or purely Schengen and non-Schengen common issue.