Final Proof or Serial Number - which first?

[Ron Wood]

That just leaves us with this aberrant gun, and the question of why it got its barrel extension SN after final proof. I haven’t seen a persuasive explanation of that just yet. And yes I saw Don’s comment the “ … left chamber number was added much later… “, but that just belabors the obvious (that the barrel extension was applied after proof) and don’t address the question of “why?”

Why?...Because the barrel extension serial number was added when the gun was modified for police use and the police numbering system followed the military style of exposed serial numbers. Originally the gun was a 1920 Alphabet commercial with no serial number on the barrel extension and hidden (on the bottom) numbers on the side plate and take down lever. These also were re-numbered in the exposed military style when the gun was modified for police service

Let’s remember that both military and Alphabet DWM commercial had the barrel extension serial number in the same place; on the left barrel extension flat. The only thing unusual about the barrel extension SN on this gun is it was struck over the existing commercial proof.

Nope...Alphabet commercials did not have the serial number on the left barrel extension flat.

Which brings us full circle to the question, “why?” I look forward to reading the speculations.

The "why" has been pretty much explained in the previous posts. The reason it seems aberrant to you is that you were of the misunderstanding that an Alphabet commercial was serial numbered on the left receiver flat...it wasn't, only the Crown/N was applied to the receiver flat.

ADDED:
Darn, Don got the answer in while I was typing!