No SRS "hit" for Krag #28828. But, that number is surrounded by a large number of model 1896 carbines in the SRS data.

Closest neighbors are #28823 and #28831. Both are model 1896 carbines turned in by 9th Cavalry on 06/14/1900.

No assumptions can be made on numbers being 'close'.
Because it is not listed pretty much guarantees that #28828 did not go to the 9th Cavalry.

Check your number very carefully with a good magnifying glass. It is very easy to misread Krag serial numbers. (In my experience, 3's, 6's, and 8's often get misread).