The Tanners conclude the Cowdery "Defence" document is probably a forgery.
Jerald and Sandra Tanner, A Critical Look: A Study of the Overstreet "Confession" and the Cowdery "Defence." (Salt Lake City, UT: Utah Lighthouse Ministry, 1967), 31
CONCLUSION. After carefully examining the evidence, we have come to the conclusion that the "Defence'" is probably a spurious work, written sometime after 1887- i.e., after David Whitmer's pamphlet appeared. Until an original copy or a contemporary reference to it is found, we must regard it as spurious.
Perhaps some of our readers will have some information concerning the "Defence" or the Overstreet "Confession" which we are not aware of. If so, they can write us at: Box 1884, Salt Lake City, Utah.