mark/proof app sequence?

[alvin]

After reading "PROOF AND INSPECTORS MARKS, 1911" on page 134 of Luger Story, I am a little confused on the mark/proof application sequence.

According to the description, four symbols on the right side of the receiver, from left to right:

1) Left letter -- Checked after dismentaling. Principal inspector's mark;
2) Center letter -- Final assembly checked by a government inspector;
3) Right letter -- Accuracy checked;
4) Proof Eagle

It's not clearly stated in the book the appropriate mark/proof application sequence being

2, 1, 4, 3, or
1, 2, 4, 3, or

Or, my understanding of the text could be wrong, were they applied in some other sequence? Thanks for the help!

=====

Was the center letter applied before or after the left letter?