Is there any basis for the ordering of the L-points? Specifically, is there any particular reason for choosing L1 as the first L-point?
The points are numbered according to their Jacobi constants. The zero velocity curves open first at L1, the libration point with with the lowest energy (highest value of Jacobi.) They open next at L2, and then at L3. The ZVCs leave the plane at last at the L4 and L5 points simultaneously.
JC_L1 > JC_L2 > JC_L3 > JC_L4 = JC_L5