You say your Nan bought these three figurines at different times. But, when she bought the first one, did the company know that she might be buying the other two? If so, they might say that they simply reserved for her No. 1157 of all the figurines available. Alternatively, knowing that she already had No. 1157 of the first figurine, they may have numbered the others to match. Incidentally, I'm not sure these companies produce 5,000 figurines (or whatever) at the outset. They probably wait for the orders to come in, and produce them accordingly.