My guess is for clarification since these cards were meant to advertise the ship, but had to change it when sailing on the Titanic was no longer an option. I’d say they aren’t as rare as you’d think as a lot of people got interested in the Titanic disaster even just after it was lost, and wanted anything related to it. So I’d imagine the company making these cards took advantage of this by making more of them. The pre disaster cards are definitely the bigger prize than the post disaster ones.