As I'm standing in A16-20 I frequently hear "they're just boarding A now, you're in B/C" and then they move out of line. When I approach A16-20 I mention my A16ish number and sometimes the person(s) in that slot show me something higher than 20; I stand in front of them. Two flights ago there were no A1-15 pax as boarding was about to start. Two girls walked up and stood at the A10 Pillar...they certainly didn't have A10 as there were no other A1-10 pax. You've never seen anyone out of position in 100 flights?