Just because it is a 24/7 server doesn't change anything. It still works alot like singleplayer. So new NPCs are always appearing, otherwise we'd run out. NPCs appear and disappear all the time. Same thing happens to commodities sitting in space. If you destroy a NPC train and jump to another system and come back. Unless there was another player sitting there, those commodities would be gone. This is what happens when the credit card trick "fails." Its not foolproof. Its more prone to error than success.