Case Identifier - issue with sequential order

I have 2 examples so far where the customer is calling to complain that their case identifiers are not going in sequential order. Ticket 78368107 the order of 001, 002, 003 & then jumped to 104. Ticket 78284028 the order of 9, 10, 11, 12 & then jumped to 15. The can be corrected by either the user or the support team, however it save time & frustration if this worked correctly.