Archivists sometimes struggle to decipher words in the vast body of documents that Mandela penned, and he often jotted an acronym that nobody, not even the former South African president in later years, has been able to explain.
Now, some of the words that Mandela wrote, which help define the man who led the fight against white rule and became president after apartheid, are on display at the Nelson Mandela Foundation, which today unveiled a public facility.
Mandela, now 95 and critically ill, wrote prolifically during his storied career.
"Long Walk to Freedom," Mandela notes his copy of the book manuscript was confiscated by authorities, but applauds fellow prisoners with "unique calligraphic skills" who helped get the original manuscript out of prison.
Mandela was a lawyer early in his career, and some letters to family from prison balance sadness with hope and optimism, with carefully chosen words.
"He doesn't shoot from the hip," said Razia Saleh, a senior archivist at the foundation.
"Madiba hasn't been able to tell us what it means," Saleh said. "So that's a mystery. Maybe somebody can solve it at some point."
The former president's orderly handwriting stems from his education in Christian mission schools, though it's sometimes hard for archivists to make out letters such as "s'' and "h'' in Mandela missives.
"We've transcribed his desk calendars, and sometimes we battle to make out words," Saleh said.
"There isn't much that survived from his early childhood. There's no photograph. We don't have a birth certificate," said Saleh. The stone, she added, is "one of the few things that's tangible, that links us to Madiba's early life.