Well, 264Magnum, you rang some bells to me. I have had (and still have) several early 1600 Std/4100 and they all have the dovetail, but now I recall some 4000 did not (I prefer the straight comb stock for these "lightweight rifles). I have one 1600 in my hands, right now, from 1954 (s/n 176###) and it gets the dovetail.... see pic below.
Can you point me out to which ad you are referring to? The only ad I have that shows a 4000/4100 without the rear sight is the Tradewinds of September 1956 titled "Kalitet Handverk" and this would be the correct one for Kamlooky's rifle.
From "the records", it seems that these "no dovetail" are "4000" 'til about S/N 208 ###, the 4100 all having rear sight dovetail (or rear sights). There was many more 4100 sold than 4000.
I'll try finding some time to post the pic of the 1956 ad tomorrow or so.
BTW, Skydevaaben site is just a numeric copy of the small HVA Museum book and contains all the errors / omissions (like the 4000/4100 infos) and we have a wide range of pre 203 ### rifles known (including a bunch of 7X57) , all from the year 1956 (from late 1955 -early 1956 production, it appears).
The alloy trigger guard only appeared around 1958 (S/N 220 000) and in the Tredewinds ads below, you can see they all show rear sights;
Tradewinds 1958 / Model 4100
Tradewinds 1955 / Model 4100
Tradewinds 1957 / Model 4100
"Lightweight" of 1954