your fandom is historical, and the sum total of historical documentation on your main character's life could maybe fill two pages.
Depending on the length of this letter, it might double the amount of contemporary documentation we have about Shakespeare's life.
If your fandom were, say, the life of Henry VIII, the appearance of a document no one knew about would be more common. But it would also be less likely to completely overthrow the understanding of Henry VIII's situation. Because the first thought I had on hearing about this letter is 'so Shakespeare DIDN'T just leave his wife in Stratford and never look back'.
[Haven't read the research. Have read The Guardian article about it, which wanted to compare the situation to one in The Comedy of Errors. So my second thought was 'do the timelines match up for this to be something that Shakespeare then put in his play?' Then again, 1607 was pretty late in his career, so probably not]
This is what happens when....
Depending on the length of this letter, it might double the amount of contemporary documentation we have about Shakespeare's life.
If your fandom were, say, the life of Henry VIII, the appearance of a document no one knew about would be more common. But it would also be less likely to completely overthrow the understanding of Henry VIII's situation.
Because the first thought I had on hearing about this letter is 'so Shakespeare DIDN'T just leave his wife in Stratford and never look back'.
[Haven't read the research. Have read The Guardian article about it, which wanted to compare the situation to one in The Comedy of Errors. So my second thought was 'do the timelines match up for this to be something that Shakespeare then put in his play?' Then again, 1607 was pretty late in his career, so probably not]