But they weren't contemporaneous. They had to be at least 22 years after the events.
There are at least half a dozen earlier accounts clearly refering to Montague John Druitt (whose name did not become public until the 1950s). The earliest in January 1889, when the head of the Whitechapel Vigilance Committee raised concern about police patrols in Whitechapel being reduced and was told "off the record, The Ripper is dead"
That’s the point, the notes in the margin that I saw, and as related by the curator, the notes were contemporaneous. . .as in written in the margins at the time the book was published. Perhaps I could have been more clear.
Nonetheless, the Black Museum has other evidence not shared publicly and the Black Museum has shared its evidence with various writers. They simply choose to perpetuate the myth.
Now, I have been there, I saw the evidence in the museum. I choose to believe my own eyes and the expert testimony of the curator at the time of my visit, as opposed to some writer looking for book sales.