Many of the Union soldiers who were killed in western Arkansas were reburied in the National Cemetery at Memphis Tennessee. The story goes that as the soldiers were buried, their names were written on "chalk boards" (large slates) that wre kept at the end of each row of graves. Apparently, the majority of the "unknown" graves WERE known. But a rainstorm came through unexpectedly and washed off the names from many of the slates, resulting in the loss of knowledge of who was buried in those graves.
So much for a paper trail!

Mahlon