The right month to place even greater emphasis on studying the Confederacy is March.
But, his "error" is something historian Barbara W. Tuchman would have understood. In her 1981 book, Practicing History: Selected Essays, she wrote that "Leaving things out because they do not fit is writing fiction, not history."
In that regard, Confederate sympathizers have been writing fiction about what the Confederacy stood for ever since Robert E. Lee surrendered to U.S.Grant at Appomattox, Virginia April 9, 1865. Governor McDonnell's choosing the wrong month was as deliberate as his initial omission of any reference to Virginia having been a slave state; and to the Confederacy having fought the war in order to maintain slavery, and as his implying that Virginia was then an all-white state, when in fact in 1860 blacks, both enslaved and free, comprised nearly half of its population.
But then, the contortions of the Republican Governor's original proclamation are entirely consistent with the record of racially-coded politics the erstwhile "Party of Lincoln" has employed for the last four decades.