Dick Hosmer wrote on Mar 14^th, 2019 at 2:22pm:

There are some things that, in my opinion, SA would not have done: 98 bolt in "96" receiver, rifle sight on a carbine, etc. Sorry, but that's my take.

  When you find your copy of Mallory 2, check page 78, right column under topic of Major Variations:  "Most Model 1896 carbines will be found with a Model 1896 rifle sight, rather than a carbine sight; and although there is a good supply of Krag spare parts, Model 1896 carbine rear sights are practically unobtainable.  No reason has been found in the Ordnance records for this situation."   Then check Brophy, page 54: "It is likely, though, that during the late years of the Krag, the Model 1898 and Model 1901 carbine rear sights were used as replacements.  Records do not indicate that rifle sights were ever used on carbines."  This would agree with you and some of us as well.

I don't have access to Mr. Farmer's work, but I would be interested to see if the above two statements are referencing the same record or if there is yet another possible explanation.