Q, while this is not an answer to your question about the earliest earliest verifiable printing of the song "O Freedom/O Freedom over me", I thought you and others might be interested in this quote from Maud Cuney-Hare's 1936 book "Negro Musicians And Their Music"
{Da Capo Press reproduction of the original printed by The Associated Publishers, Inc. from a copy in the Indiana University Library collection; pps 68-71}:

"There are now many collections of Negro folk songs available. In the songs herein noted are those that are best known and which might be regarded as "master songs". They are chosen with the hope that the history of each particular one may be of value to serious students. Here are songs of triumphant faith, of solace and comfort, of tribulation, and secular songs pertaining to labor and recreation, love and childhood.
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"Swing Low, Sweet Chariot", an American Negro Spiritual" in the pentatonic scale, noted in "Fisk Jubilee Songs, 1871, offers a key to this development. The variantgs of this song are "Good Ole Chariot", "Swing Low, Sweet Chariot" {Hampton{ and "The Danville Chariot".
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William Arms Fisher, who has given the melody a setting for solo voice and piano, tells an interesting story about the song, which was told to him by Bishop Frederick Fisher of Calcutta, India, who has recently returned from Central Africa. He relates:
'Bishop Fisher stated that in Rhodesia he had heard the natives sing a melody so closely resembling "Swing Low, Sweet Chariot" that he felt that he had found its original form'...

In American, it is told that the song arose from an incident which happened to a woman sold from a Mississippi plantation to Tennessee. Rather than be separated from her child, she was about to drown herself and the little one in the Cumberland River, when she was prevented by an old Negro woman, who exclaimed, "Wait, let de Cgariot of de Lord swing low and let me take de Lord's scroll and read it to you". The heart-brokened mother became consoled and was reconciled to the parting. The song became known with the passing on of this story, which seems more legendary than real.

Among these songs several others of unusual importance should be noted. "My lord Deliverd Daniel" in major key of G, with a variant from Florida "O Daniel," and another title of the original in Kentucky. "Wrestling Jacob" with four variants, "My Lord What A Morning"", from the Southeastern Slave states, "A New Hiding Place" with the same theme, "I Want To Be Ready", from Kentucky, with such variants as "Walk Jerusalem Jes Like John" and "Walk Into Jerusalem Jest Like John", and "When I Come To Die". Next tere was the "Old Ship Of Zion", from Maryland and Virginia, with many variants like "Don't You See The Ship a Sailing?" and "In the Old Ship Don't Weep After Me", "Inching Along," "Keep a Inching Along," from Alabama, "Go Down Moses", an interpretation of Hebrew History with varinats from Virginaia and the Bahamas. As the Lord delivered the Jews so would He the Negroes. We note also "Did not Old Pharoah Get Lost", "When Moses Smote the Water", and "Turn Back Pharoah's Army", "When the Lord Called Moses," belonging to this same class.

Of another type was "Nobody Knows The Trouble I've Seen" or "Nobody Knows the Trouble I See", or "Nobody Knows the Trouble I See, Lord," originally from the Sea Islands. "Sometimes I Feel Like A Motherless Child," from Mississippi, "I am Troubled in Mind,", "O My Body Racked Wid de Fever", from Georgia, with a version "I'm a Trouble in de Mind," from Port Royal Islands, "Don't Be Weary Traveler", from Virginia, "Let us Cheer the Weary Traveler", from Kentucky; "I Long To See the Day", of major node, probably known first from the Bahama Islands; "There's A Meeting Her Tonight", probably noted first form Port Royal Islands; and "My Way is Cloudy", found in several places.

Then there are two distinct types of slave songs, although there are but few songs using the practice of slavery as a theme in the text. Some of these are "Many Thousands Gone", "No More Auction Block For Me", and "Is Master Going To Sell us Tomorrow?". Then there are such songs as "O'er the Crossing.", from Virginia, with variants as "My Body Racked wid Fever" from Port Royal Islands, "O Yonder's My Ole Mother,", and "My God Called Daniel". Next one notes "The Gospel Train" with variants like "Get On Board", from the Bahamas. and "From Every Graveyard" and "Get On Board Little Children", heard in many places. Widely reported, too, is "Roll Jordan Roll", in E major showing use of the flat seventh, a variant of the Bahama song, "I Long To See The Day". Well known also was "Somebody Knocking at Yo' Door", with the version, "O Sinner You;d better Get Ready".

There are striking examples of Burial Hymns developed from the custom of sitting up and singing over the dead. Among them are "These Are My Father's Children", noted with the variant, "Siiner in de Morning," which has two other variants, "These Are My Father's Children", from North Carolina, and "The TRouble of the World". A fine funeral song is "I Know Moon Rise", reported frirst from Georgia. Impressive also are "Graveyard", and "Lay This Body Down", first noted from Port Royal."