Our first time at Captain's table was 1997 on the Majesty. It was dh's birthday but I don't think that was it. We were with friends and the 3rd couple at our table were new to cruising but he did work for one of the airlines. None of us had any status. One evening the head waiter came to our table and asked if we had any p,and for the next evening. We all said no and he told us we would be eating with the Captain the next evening. It was a great evening.
In 2015 on our Baltic cruise we had a free upgrade to a GS, remember those days, and mentioned to the concierge in the lounge that we'd love to do Captain's table again. We were invited but since there was a last minute itinerary change because of weather the Captain couldn't make it. The f&b director, whose parents were onboard and who we became friends with, hosted the evening. It was nice.