“It’s always been clear that Shakespeare of Stratford and ‘Shakespeare the player’ were one and the same,” Mr. Shapiro said. “But if you hold the documents Heather has discovered together, that is the smoking gun.”

Ms. Wolfe’s discoveries began in the archives of the College of Arms in London, home to 10 heralds who are still charged with researching and granting coats of arms — arcane territory where many literary scholars might fear to tread.

“Looking through the minutiae of the College of Arms is, even for Shakespeare scholars, almost unbearable,” Mr. Shapiro said. “We really owe Heather a debt of gratitude for wading in.”

Ms. Wolfe said she began wondering if there wasn’t fresh material to find there when she looked through a book edited by Nigel Ramsay, a historian at University College London, with whom she curated an exhibition on heraldry at the Folger in 2014. On one page, she was startled by something she had never seen before: a sketch of the arms with the words “Shakespeare the player,” or actor, dated to around 1600.

A similar image with the same text — a copy dating from around 1700 — has long been known to Shakespeare scholars (as well as to authorship skeptics, who generally dismiss as unreliable any evidence dated after 1616, the year of Shakespeare’s death). But this earlier one, from the College of Arms, seemed to have gone unremarked on.

Ms. Wolfe started digging there and in other archives, and so far has gathered a dozen unknown or forgotten depictions of the arms in heraldic reference works called alphabets and ordinaries. “I just started finding them everywhere,” she said.