I'm a Krag 'Sight Junkie' and your pictured rear sight is a bit of a riddle. It is a combination that should not really exist.

The right knob appears to be an S&S Firearms replica.

The base appears to be a real model 1898 carbine-sight base.
The elevation slide may be correct, (with no plunger hole on left side).

I believe the leaf is a rifle leaf with a faked "C", added. (The blurry "C" is not quite in the correct location. The three notches appear off-set slightly to the right).

Springfield Armory salvaged the 1898 rifle leaf by adding serrations on the left edge and rounding the corners of the eye-piece, to eliminate the outside notches.
The altered leaf was put on a 1902 base to make a variation of the 1902 sight.

I believe 1898 (rifle and carbine) sight-bases ultimately became scrap.
Some were used on the surplus parts market to make non-official arms and 'mix-master' sights. (Bannerman, Stokes-Kirk, S&S Firearms).

The 1898 'three-notch' carbine rear sight is pretty rare. (The notches on the carbine eye-piece are centered).
The carbine leaf, like the rifle version, was probably salvaged to make some 1902 sights.

An example of an 1898 (correct carbine?) eye-piece, that was later 'altered' by rounding the corners, is listed on Grandpa's Gunparts. It is rather expensive.

I wonder if Cadcord's unusual rear sight was possibly put together by S&S Firearms as a "replica"?

Attached altered photo highlighting notch 'off-set' and approximate correct "C" location.

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