B side is a commentary on "Old Soldiers Never Die (They Just Fade Away)", the speech General Douglas MacArthur made upon retiring after President Truman relieved him of his command in the Korean War.
The Korean War prisoner exchange called "Operation Big Switch" took place from August to December 1953. At its end 23 Americans chose not to go home. Given 90 days to change their minds, two did so, leaving 21 men who remained in North Korea and then went on to China. That means the earliest the B-side could have been written was late December 1953 / early January 1954. BTW, of the 21 all but two had left China by 1966.