Is it known how it happens that the 2001 Muggle-oriented reprint of Fantastic Beasts and Where to Find Them carries an introduction by Albus Dumbledore, seeing that he died in 1997? Conversely, if the book was already in the works before his death, is it known why it took until 2001 to have it published?
Dumbledore wrote it before his death but after November 24 1994.
The foreword for Fantastic Beasts and Where to Find Them isn’t the only thing Dumbledore wrote that was published after his death. Dumbledore had written a set of notes for The Tales of Beedle the Bard, and left them in his will to the Hogwarts Archives.
“This similarity of outlook notwithstanding, it was a surprise to discover a set of notes on The Tales of Beedle the Bard among the many papers that Dumbledore left in his will to the Hogwarts Archives. Whether this commentary was written for his own satisfaction or for future publication, we shall never know; however, we have been graciously granted permission by Professor Minerva McGonagall, now Headmistress of Hogwarts, to print Professor Dumbledore’s notes here, alongside a brand-new translation of the Tales by Hermione Granger.”
- The Tales of Beedle the Bard
Those notes seemed to have been made eighteen months before his death in 1997, though the book was published in 2008.
“It seems only right to make one small, additional comment on Professor Dumbledore’s notes. As far as we can tell, the notes were completed around eighteen months before the tragic events that took place at the top of Hogwarts’s Astronomy Tower.”
- The Tales of Beedle the Bard
Therefore, it doesn’t seem so implausible that something similar happened with Fantastic Beasts and Where to Find Them as well.
Though nothing states when Dumbledore’s foreword was written, we can further narrow down the time period by looking at Harry’s notes. Harry’s notes could have been written over the years since he first got the book, but the latest one would have had to be written after he encountered the dragon in the Triwizard Tournament.
The only time Harry ever encountered a Hungarian Horntail was at the First Task during the Triwizard Tournament, so he had to have written that particular note after that - meaning the notes would have been copied sometime after that. We have an exact date for the First Task - November 24th, 1994.
“The first task will take place on November the twenty-fourth, in front of the other students and the panel of judges.”
- Harry Potter and the Goblet of Fire, Chapter 17 (The Four Champions)
So, Dumbledore most likely wrote the foreword between November 24th, 1994 and his death in the summer of 1997.
The delay in publishing may be because it’s meant for Muggles.
Perhaps the reason it took these books so long to be published is because they’re wizarding books being published for Muggles. Attempting to make wizard books available to Muggles is likely quite difficult to get approved, and would have to be done very carefully to avoid violations of the Statute of Secrecy. It may take a while to navigate the obstacles to getting a wizarding book approved and safely publishable for Muggle readers.
It’s likely to be much more difficult than publishing a book by wizards for wizards only. Something like that would almost surely have to be approved by the Ministry first, which could certainly add to the time it takes. In addition, there are surely wizards who would not want a wizarding book published for Muggles, some of whom may be in positions of power where they could try to stop or impede its publication. Madam Pince, the Hogwarts librarian, was certainly very unhappy at the thought of making Quidditch Through the Ages available to Muggles.
In addition, around the time Dumbledore would have written the foreword, the wizarding world would have been entering a time of turmoil - the Dark Lord regained a body and began trying to take over. Those who supported the Dark Lord surely would not want to approve anything of the wizarding world being given to Muggles, and those who would approve of the idea likely would have higher priorities. The Ministry was busy trying to deny the rise of the Dark Lord, then was controlled by the Dark Lord. Neither of those situations would make them particularly willing to publish a wizarding book for Muggles.
The only way to make the timeline work is if it was written before Dumbledore's death, naturally. Based on in-book clues, Dumbledore wrote the foreword between 1995 and his death in 1997.
Dumbledore refers to the fact that it is a reconstruction of the textbook used by Harry Potter. At various points in the book, Harry leaves snarky comments. From the comment left under the entry for Mermaid ("ugly"), we know it was written at the latest after the Second Task in Harry's fourth year in school, in February 1995.
But missing are any notes under the creatures Harry encounters in the fifth book (most notably, thestrals). That suggests the book was copied in between his fourth and fifth years-- which of course was the point the series was at when Rowling published the book. What a coincidence!
Alternatively, the lack of further notes might be attributable to Harry maturing at the end of his fourth year after the return of Voldemort. It might be that Harry gave up the book in September 1996 after he stopped studying Care of Magical Creatures.
As for the reason for the delay? Well, we're not going to get a canonical answer obviously. But there WAS a massive war that lasted until June 1998. It could simply be that it took three years until the Ministry could be bothered to worry about trivial issues.