The M1898 was adopted on May 9, 1898. IT was shipped to Cuba in mid july, with regular units recieving them first, then USV, then state units. The 1st USV recieved theres sometime during the 1st week of August. This was only for those units in Cuba, IE troops A,B,D,E,F,K and L recieved the new uniforms, Troops C,H,I and M retained the 1884s back in Florida.
These were the 1898 1st Issue, with the Branch colors on shoulders, cuffs and collars. Only Those units in Cuba recieved this uniform, by July the uniform board had modified the 1898 to a simpler cut, with a conventional back, kahki collar and cuffs, and clip on shoulder tabs in branch colors. This 2nd issue, also known commonly as the M1899, would be issued later to those units deployed in the pacific, and remain general field issue with minor modifications until 1911. The 1884 also remained in the locker for fatigue issue until 1911!
There was a good deal of mixing with various units moving to different theaters around the centurys turn. The War department even bought British field Kahki unforms in Hong Kong for issue, as they were considered Very Close in style to the American uniforms, with the addition of US insignia and other accoutrements.
The 1884 was modified by enlisted only by the addition of Rank on sleeves and appropriate Leg stripes. Officers had more latitude, and there were seveal different variations even within the 1st USV themselves, though the most common seems to be the conversion of the Collar to a standing collar of Branch color, False cuffs in Branch color, Leg stripes, and clip on officer shoulder boards.
Highly reccomend "Cowboys in Uniform" for its collection of data on the 1st USV.