A volunteer in Britain made an exciting find last year that was just revealed:

Michael Scurr has been volunteering at Britain’s National Archives for the last 11 years, spending his Thursday mornings painstakingly cataloging documents for the benefit of future researchers.
Then one day last May the retired insurance executive made a discovery of his own while sifting through the letters of an 18th-century Royal Navy captain.
There, attached to a report on the capture of the American privateer Dalton on Christmas Eve 1776, was an enclosure identified only as “another paper.” Carefully unfolding the document, Scurr stopped when he saw the word “Declaration” printed across the top…
Researchers at the National Archives have since identified the document as a rare early copy of America’s founding document, printed just days after the original was signed on July 4, 1776, to spread the news that 13 rebellious North American colonies had severed ties with Britain.
It is one of just 11 original copies of the so-called Exeter printing of the declaration that are known to exist, and the only one identified outside the United States, the National Archives said on Thursday as it unveiled the find ahead of this weekend’s 250th anniversary of American independence. This version was printed in Exeter, New Hampshire, July 16 to 19, 1776.
I have benefited greatly from researching in several archives. Materials are catalogued at various levels of detail, perhaps just having a title on a box or folders that point to a theme or a person or a time period. And even with more detail, it is still fun – and sometimes dull – to go through what is available to see what is really there.
I cannot imagine what it would feel like to discover such a rare document. I use another example of an unexpected find in teaching about doing archival research. Such finds can help clarify historical narratives or reveal new narratives. With this find last year in England, I imagine it can help us better understand how news of the Declaration spread. With revolutionary activity before the document was signed and announced as well as after, how did the news spread and what exactly did that lead to? The date of July 4th may seem obvious now but it would have taken days for people to learn what had happened and respond.