In August 2021, a mysterious package from Sarasota, Fla., showed up in Nicole Archer’s mailbox in Manhattan.

Dr. Archer hurried upstairs to her cramped Chelsea apartment with the thick envelope in hand and tore it open at her dining table, revealing a legal document she had wondered about for months.

She knew that a beloved college professor had bequeathed her something in her will. She was expecting a modest gift — enough money for a fancy dinner, perhaps, or one of the beaded bracelets the professor liked to make by hand.

But when Dr. Archer, 49, saw the number on the last page — $100,000 — she thought there must be a misplaced decimal point.

“I truly, honestly believed that I read it wrong,” she said. “I remember following the number with my finger, making sure I understood how many zeros it was.”

At about the same time, 30 other people across the country received similar letters, sent at the behest of a professor whose class they had taken years earlier.