Ken Burns said of his "The Civil War" documentary that it took much longer to make than it took the actual  American Civil War (from Fort Sumter to Robert E. Lee's surrender of The Army of Northern Virginia at Appomattox Court House) to be fought.  I can perhaps give you and him a pass on the correct number of black Union soldiers, but you're not suggesting that getting right Abraham Lincoln's age at the time of his death should have been so difficult are you?  Especially since Burns (acknowledged by most people to be no dummy) took at least eight years to finalize "The Civil War."