"Almost any Krag rear sight is "correct" on an 1898 rifle - they went through a lot of changes and overhauls."

It is a VERY long story, involving such things as a bitter political battle between two ordnance department officers, some unintentionally (due to weather!) overloaded ammunition, inability to manufacture replacemnts in a timely manner, and just plain choice and/or chance. In SOME cases it is possible to determine what sight SHOULD have been on the rifle as made, in others it is not so clear.

The collector attitude today seems to be that if the sight appears to match for color and wear, is fastened with un-buggered screws, has the proper matching handguard, and does not egregiously violate any of the known parameters, the rifle is "accepted" without $$$$ penalty.

I see nothing "wrong" with your gun. Supposedly, all rifles being put into 'final' storage, when rendered obsolete by the '03, had their sights changed (if not already so equipped) to either the M1901 or M1902 rear sight.