The accident was blamed on modifications made to the bolt - the nut had been shortened, and an adhesive seal had been broken - but it had never been established who was responsible for them, or when they were made.
The hoist had not been checked by its supplier since the warranty expired six years before, while the company contracted to check the device, BV Medical, did not record any faults on it aside from adjusting its legs.
The lawyer acting for BV Medical accepted the installation of the scale was, in hindsight poorly, implemented.
Mrs Wilson's death had resulted in BV Medical introducing a new checklist process, where any problems are noted with photographs and recommended changes, and rest home owner Bupa New Zealand removing weigh-scale hoists from its facilities.
But an investigation by the old Department of Labour found there was insufficient evidence to prosecute and that the bolt was not an obvious hazard and could not have been spotted.
Mrs Wilson's family could not accept that report and appealed for a coronial inquest, which was held by Rotorua Coroner Dr Wallace Bain last year.
In findings released today, Dr Bain criticised the care that was provided to Mrs Wilson, but found there was not enough information to determine who was responsible for the faulty bolt.
"This is indeed a very sad case and demonstrates the need for high standards in checking medical devices," he said.
"Patients and families put their whole trust in the health system and the health professionals who are caring for them and operating various medical devices and looking after them."
In the case of Mrs Wilson, Dr Bain said the care given to her had fallen short, and those involved were following procedures that they thought were sufficient and acceptable in protecting the safety of their patient.
"This case has sadly demonstrated that the procedures being followed in respect of the inspection and operation of medical devices fell short of the standard and that was owed to Mrs Wilson and her family."
While it still wasn't clear when and whom had modified the nut or broke an adhesive seal on the bolt, there was sufficient information to conclude that its poor standard had caused the accident, and that what had happened to Mrs Wilson was "'inevitable"
Dr Bain found the best way forward was to list the recommendations made by lawyers for Mrs Wilson's family, BV Medical and the Ministry of Business, Innovation and Employment.
They included:
*A running log book should be kept for every piece of biomedical equipment in rest homes, and any changes should be checked and approved
*Each piece should be subjected to a full acceptance test, those with moving parts should be serviced more regularly, and only qualified technicians should be able to service them
*Rest home staff who use the equipment should be trained on their safe condition and how to conduct a visual check of it before each use
*Whenever faults are noted, the equipment should be immediately removed from service
Speaking from Australia, Mrs Wilson's grandson, Mathew Warren, said he was pleased the process had further established that his grandmother had been failed.
"In the end, both [Bupa and BV Medical] did not provide adequate care to my Nana - if they have had, she wouldn't have died," he said.
"The coroner's process was obviously a bit weak in holding people to account, but [Dr Bain] has gone some way in saying that Bupa didn't provide the care required and that BV medical did not service the equipment to the standard that was required."
Mr Warren said he would be speaking to his lawyers about whether to go any further, but he expected the findings would end what had been a long, expensive and trying process for his family.
"It's been a good process in that, if we hadn't gone through it, we still wouldn't have known what happened - or didn't happen."
Despite the recommendations, Mr Warren wasn't confident that the accident would not be repeated.
"It probably will happen again, whether it's a year, or two years, but hopefully this will set a little bit of a precedent for the process, and what people should be following."
