very helpful post. fyi on a Sept 2023 cruise in Ireland the Non Refundable OBC I received for cancelled ports could NOT be applied to the DSC (mandatory service charges / tips). I had asked our butler if we needed to do anything special to apply the NR OBC, and he said 'no', it would apply automatically. That answer was not correct. We had charged photos and discretionary tips in specialty dining restaurants, and the $100 NR OBC was not applied to those items.