AMSTERDAM — In a letter to her grandmother in 1940, composed before she went into hiding here, 11-year-old Annelies Frank recorded a detail that surely seemed of little consequence at the time.

“Daddy is very busy in his office,” wrote the young correspondent, in a script already elegant. “He is moving to the Prinsengracht, and I’ll go and fetch him from the tram as often as possible.”

It was there, in the annex above her father’s office on the Prinsengracht, or Prince’s Canal, that her family would hide for more than two years from the Nazi occupiers, beginning in 1942. And it is there, in the museum that now occupies the building, the Anne Frank House, that visitors can view that letter to her grandmother.

But custody of that note, along with 10,000 other similar archival documents and photographs, is at the center of a bitter legal fight between the House and the Anne Frank Fonds, the other foundation most closely involved in the telling of Anne’s story. The Anne Frank Fonds, founded in 1963 to manage the copyrights to the Anne Frank diary, lent most of the disputed archives to the House in 2007 and has sued for their immediate return. House officials said they believed the loans would become permanent. A verdict is expected in the coming weeks.