The April 5 date written in the book is not unlikely. The book may have been loaned out when it was captured, and there is a very explicit mention of just such an incident, consistent with the April 5 date, in: OR, Vol. 34, Pt. 1, Page 772:

PINE BLUFF, ARK., April 9, 1864.
Major [Mark] McCauley has just come in, having been out on a five days scout. He went through Monticello and Long View to Hamburg, to within 15 miles of the Louisiana line. Had a skirmish; killed 2, and captured 2 lieutenants and 17 men. He reports the country this side of the Saline as abandoned by the enemy with the exception of a few straggling bands. Heard at Monticello that General Steele had advanced to within 6 miles of Camden. I will send the Eighteenth Illinois on the first boat.
POWELL CLAYTON
Colonel, Commanding.