My source comes from the book "The Confederate Order of Battle" Vol 1, by F. Ray Sibley, Jr.

Page 399 in the endnotes had this to say on the 51st Virginia infantry regiment.

"The remnants of the 51st Va joined Gordon's units sometime after 2 March 1865, and lost their battle flag 25 March 1865, at Ft.Stedman."

His source was "Davis, 51st Va, page 42."

Hope that helps someone,

Have a good day

Shawn Prouty