Researchers have confirmed that a manuscript of the Declaration of Independence discovered deep in the archives of a British aristocrat is one of just two known parchment copies of the famous document in existence.

A team of researchers led by two Harvard academics found the manuscript almost three years ago at the West Sussex Record Office in the English city of Chichester, Agence France-Presse reported Wednesday.

Dating tests completed earlier this week finally confirmed the researchers’ hypothesis that the Sussex Copy, as it has been dubbed, was produced some time in the 1780s, just a few years after the original declaration on July 4, 1776.

Although there are other printed and handwritten copies of the declaration, the Sussex copy “is the only other contemporary manuscript copy of the Declaration of Independence on parchment apart from the signed copy at the National Archives in Washington DC,” the West Sussex County Council said in a statement.

The parchment is thought to have once belonged to Charles Lennox, the Third Duke of Richmond. Lennox was a British army officer known as the “Radical Duke” for his outspoken support of the cause of American independence during the Revolutionary War.

The Harvard team was able to determine date of the manuscript by using several of advanced analytical methods, including multispectral imaging, X-ray fluorescence (XRF) capture, and DNA testing, the Harvard Gazette reported. The tests revealed a date — either “July 4, 178” or “July 4, 179” — that had been erased from its original position just to the right of the document’s title.

XRF tests found high iron content surrounding the holes in the corners of the parchment, leading researchers to believe that nails were used to hang it. DNA testing also revealed the parchment was made of sheepskin.

Researchers say one of the more interesting aspects of the Sussex Declaration is that the names of signatories are not grouped by state, as they are on the original manuscript. The Harvard team hypothesizes that the change was made during the Constitutional Convention to promote the idea that the declaration’s authority came from a unified national people, not a citizens of individual states.

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