Plagiarism in the ranks?

While writing the chapter on the 137th's December march from Bolivar Heights to Dumfries,
I re-read the diary of Zuri Wellman, Sgt, Co. F. His December 162daily entry had a phrase "slovenly homes" to describe the houses they passed on the way struck a chord in my memory. I'd see it before.
Sure enough, in the letter Capt. Henry Shipman, Co. F, wrote in late January to the Binghamton Republican, appeared that same phrase. As I checked further, many of the episodes in Catp. Shipman's letter were borrowed directly from Sgt. Wellman's diary. Of course, Shipman may have asked his sergeant for permission to include the daily entries in the letter written for the folks at home. Still, one wonders.
In any event, as a historian wanting to describe as faithfully as possible the events in the life of a regiment that occurred 145 years ago, it is reassuring to have not just almost primary sources (Shipman's letter written one month removed), but ultimate primary sources - entries written on the day things happened.
My thanks to the Brown County Museum, Green Bay Wisconsin, for transcribing Zuri Wellman's diary in the summer of 2006, and sharing the resulting material with me.