I'd say the liklihood of having someone on the plane with the same first initial & same 3 letters to start your last name is VERY small. Assuming that all letters appear in names with the same probability, there's a 1 in 456976 chance that you will have the same 4 letters as anyone else. Typical upgrade lists are in the 20-50 range, so that's not going to happen very often. Since we know not all letters appear regularly in names (how many of us have Q, Z, X, V, etc in your names?), lets just assume there are 16 letters that appear regularly in names... then there is a 1 in 65536 that your 4 initials will match someone else. Again, not probably going to happen on the upgrade list, but it's still possible. Ok, math class is over...