43X is internal use for ground operation purpose. Gates has a yellow line indicating the position for aircraft to park at the gate. At Gate 43 of LAX depending on aircraft parking position is slightly different. It has being few years since I relocated out of Los Angeles, but if I remember correctly, at Gate 43 there are two or three different yellow lines depending on aircraft. Each yellow line is marked “43A”, “43B”, “43X”. etc. Gate 41 at LAX has two yellow lines and it is marked in similar way.