First, a comment:

I have stared again at my copy of "The Red River Valley" from the Piper Collection at Iowa, the one bearing the notations "Nemaha - 1879" and "Harlow 1885." Previously, I gave the second line as

"I shall miss your bright eyes and your(?) smile"

Looking again, I think the scrawl may instead be "fair smile".

Second, a question:

When was the first notice of the "cowboy" version, the one with the phrase, "the cowboy who/that loves you so true"?

As far as I know right now, it was Carl T. Sprague's 1925 recording. A host of other recordings followed, including one by Jules Verne Allen in 1929.