You wrote: >>>Interesting that they were prisoners for almost 2 years!! Would have figured that they may have been exchanged earlier. <<<
July 1863 marks the collapse of the Dix-Hill Cartel, or General Exchange Agreement. A total of 1,697 paroled Confederate prisoners of war, selected on a "first in, first out" basis from the men captured at Champion Hill and Big Black Bridge in Mississippi, were paroled at Fort Delaware on 4 JUL 1863 and delivered to Confederate authorities at City Point on 6 JUL 1863. This was the last shipment of able bodied POW's to be delivered from Fort Delaware. A second shipment of some 1,800 POWs was also sent from Fort Delaware, but halted en route by order of Major General Robert C. Schenck, commanding the Middle Department headquartered in Baltimore. Challenged by the War Department, Schenck responded on 8 JUL 1863: "When two or three days ago I directed General Schoepf [Brigadier General Albin F. Schoepf, commanding Fort Delaware] to suspend sending prisoners of war to City Point, it was because I had assurances that they would immediately upon arrival be employed for defense of Richmond. I supposed this also to be the idea at the War Department when I was instructed to have acommodations for 6,000 at Fort Delaware. Shall I order General Schenck to send now to City Point those he has?" [OR, Series II, Volume 6, p92]. That same day, Schenck received a telegram from Secretary of War Edwin M. Stanton sustaining his action in halting the exchange deliveries. The POWs in the second shipment were returned to Fort Delaware. At the end of July, 752 sick POWs were paroled at Fort Delaware and delivered to CSA authorities at City Point on 1 AUG 1863. This included some of the men from the aborted earlier delivery. The rest of the returned men remained at Fort Delaware until Point Lookout opened for business in September 1863. Some remained at Fort Delaware for the balance of the war. Thereafter, only the sick and disabled were sent for exchange, and these releases were few and far between until the spring of 1865.
Conventional wisdom is that General Grant ordered the end of the prisoner exchange agreement in when he became Commander of all Union armies in the field in March 1864. The exchange process was halted by order of Secretary of War Edwin M. Stanton nine months earlier, and General Grant merely sustained and defended the policy set in motion in the summer of 1863 when he took command of the armies in the field in March 1864.