Seeking POW records of Edgar Simpson

When Ann Eliza Simpson got married in Lynchburg, VA on 4 March 1863 to her English husband, Edgar, he was a Confederate deserter (12 June 1862). But I am not able to reconcile the fact that it wasn't till 8 months later that he was 'released' from Fort Monroe after taking the Oath of Allegiance on 5 November 1863. Was there a 'day release' scheme, were 'trustees' allowed out to help on farms (as POW's were in the UK in WWII) and this is when he was able to do his courting and get married? What I want to understand is how could a supposed POW, go about courting and get married while still in custody?

In her book, ‘A World on Fire’, published in 2010, the author Amanda Foreman makes several references to the situation in New Orleans around the time that Edgar, a sailor, enlisted so I wonder if he was a willing volunteer. Though he did make a great play of his Confederate Army 'record', no mention of deserting, for the rest of his life.      ....“the extensive commercial ties between New Orleans and Liverpool reflected in the social prominence of the British Consulate…It was not the willing recruits that concerned Mure, (The British Consul) however, but rather those who were forced to volunteer whether they wanted to or not. King Cotton ruled with a brutal hand in New Orleans. British subjects were being marched to recruiting posts by self-appointed vigilantes, ‘not in twos or threes, but in tens and twenties’. “Throughout the Confederacy intense pressure was being exerted on the 233,000 foreign residents to prove their loyalty to the South.