The pathologist's report found Mrs Wilson died of pneumonia as a complication of "severe closed head injury".
The Department of Labour investigated, but found there was insufficient evidence to prosecute.
Those interviewed in the inquiry said the bolt, which appeared to have been shortened, was not an obvious hazard and could not have been spotted.
Bupa New Zealand, the company that owns the rest home, says the hoist was one of three fitted with a weigh-scale when it took over the home four years ago.
It had been supplied by Auckland-based Active Rehab in 2003 and had not been checked by the company since its warranty expired in 2004.
BV Medical, the firm contracted to check the hoist, inspected the device for the first time in 2009 and though its legs were adjusted, the employee did not record any other faults.
Documents obtained by the Herald showed the department failed to ascertain who had modified the bolt, although it was inferred that a maintenance man, since deceased, may have shortened it.
Bupa chief executive Dwayne Crombie said weigh-scale hoists had since been removed and put the accident down to an "engineering design fault".
BV Medical has also brought in a new checklist process where any problems are noted with photographs and recommended changes.
Aged Care Association chief executive Martin Taylor, who was unaware of the incident, believed there was no general issue with rest-home hoists.
But Mrs Wilson's family fear such incidents could happen again.
"This was way beyond an accident - this was unnecessary," Mrs Warren said.
"It's just not good enough. We just want a public hearing so we can ask some questions, make things better for other people, and give my mother some peace."
Mathew Warren, Mrs Wilson's grandson, has been pushing for a coronial inquiry and said the family would not accept his grandmother had died from natural causes.
"We don't want it to end with just a finding saying Nana died from pneumonia as a complication ... I still want answers."
Mr Warren said he wanted to know why a piece of equipment used every day had failed so disastrously, why it had not been maintained properly, and why the company did not get rid of it when it took over the home.
"If it was maintained to a certain standard, the bolt never would have come out like it did. It resulted in her death, it was a catastrophic event and I'm still flabbergasted about the whole thing."
Dr Crombie said Bupa had taken all reasonable actions to prevent the accident happening again.
"We don't have any unfinished business, so to speak. It was a tragic accident and I don't think there is much you could add at this point."
The company would participate in a coronial inquiry if needed, he said.
A Coronial Services official said the case was pending.
Tauranga man Geoff Harper, whose 100-year-old mother died after living with undiagnosed scabies in the same rest home, has abandoned seeking an inquest into her death, dismissing the process as a fruitless exercise.
Mr Harper found that in the past two years, just two complaints involving rest homes had got to a Medical Practitioners Disciplinary Tribunal hearing. Just three had got to a Human Rights Tribunal hearing, resulting in a total of $9500 in penalties.
But he wished the Warren family well. "I just hope they've got the fortitude to proceed."
