I don't have Edward's book with me but I looked up the report online and you are correct that the report is approximately April 28-May 7, 1864. So, it would appear, this was an error in Edward's book though it is possible, of course, the ORs is wrong. I often check the Making of America website for the ORs because they are images of the actual printed pages and because I like the boolean search. I know there are some errors in my copy on CD (Broadfoot) but I think they are limited to duplicated lines as opposed to incorrect words.
I don't think the Supplement to the ORs is avaliable electronically but you can buy them new for about $5,400 or used for $3,800. Just put it on your VISA card, scan them, digitize with OCR, and send them to me on DVDs. I'll pay for the disks and postage.
I don't own "Embattled Arkansas" but have read it and agree it is quite good and very thorough.