
The gathering took place at Black Gully, where Mr Sim had mysteriously disappeared more than a century ago.
Jocelyn Chalmers said the reunion was attended by four generations of family members who live across New Zealand.
"Our great grandfather was a farmer at Ardle Bank, Crookston, West Otago. Otago. He was married to Mary Jane (nee Fowler) and the father of Stuart, Alex, Minnie and Douglas. Sadly, he disappeared on 30 September 1923," she said.
"According to files at Archives New Zealand, my great-grandmother Mary heard him leave the house early but could find no trace of him when she went out some time later. She says in the file that she did not expect to see him again.
"Large groups of family and friends searched for him for months, at one point finding footsteps up the Blue Mountains, in a direct line up from Black Gully, which they followed before losing them."
Ms Chalmers said it was not until March 1976, when remains were found by deerstalker Ron Topping, in the Blackcleugh region of the Blue Mountains, that there was an answer to the question of where he had gone.
On the day of the memorial, Mr Topping was invited to the family gathering to talk about the discovery day.
In 2022, Ms Chalmers, a retired research librarian from Wellington, and her cousin Garry Sim, of Alexandra, began researching the story.
"I discovered three years prior to his disappearance, James, while fencing at the farm, had had an accident whereby he was struck on the back of the head by a wire strainer, causing traumatic brain damage. He was hospitalised for depression in 1923 but became increasingly withdrawn when he returned home.
"The link between brain injury and depression is now well known, but perhaps not so well understood at the time," Ms Chalmers said.
By Nicola Simpson and Jules Chin