By identical, I mean having the same signature - family, model, stepping and brand string of the CPU (which essentially identifies a CPU model uniquely)
If I'm not wrong, a CPU package goes into a CPU socket on a motherboard.
edit: oops, I forgot to add that I was looking for info related to Intel server CPUs (Xeon and similar). Nothing specific, just wanted to know whether CPU packages in servers have always had exactly the same CPUs. Thanks!