Some simple rules I live by
I generally find 1896 sights on 1896 rifles, but not always. If an 1896 does not have an 1896 rear sight I look a little harder at the rifle.
Regarding 1898 rifles: The only "wrong" rear sight on an 1898 rifle is an 1898 rear sight. Nada, zip, never. The 1898 rear sights were withdrawn from service, never, ever to be used again by our military establishments.... as an 1898 rear sight. Many of them were re-configured to 1902 format, that's fine, but the 1898 rear sight did not stay on any Krag rifles. Another wrong rear sight for any rifle aside from and unaltered 1892 rifle, is the 1892 rear sight.
Aside from that there is no right or wrong, rear sight for an 1898 rifle, while in service your rifle could have had the 1902 rear sight or the 1901 rear sight. In my view it is unlikely that an 1896 rear sight would have remained on an 1898 rifle even tho some of the early 1898's sported them early in production, but that's another story altogether.
"A man with a tractor and a chain saw has no excuses, nor does he need any"
Me. "Consistency is the hobgoblin of little minds" Emerson "Consistency is the darling of those that stack wood or cast bullets" Me.