A surgeon who treated him just before he died in 2019 was so concerned he asked the Coroner to investigate, saying his death may have been avoided if action was taken earlier.
There was deep necrosis (dead tissue) and an infection in his bones around the wound.
The Health and Disability Commission took over the investigation and has criticised his care at Dunblane Lifecare in Gisborne, which was operated by Heritage Lifecare at the time.
Its report found the man - referred to as Mr A - went into the home at rest home level care after he was unable to be at his own home.
He had just started to need a wheelchair and had lived with several injuries since a fall from a truck in 1971.
In his second month at the home a nurse noticed an "injury by his bottom", at the sacrum, and, shortly after, his granddaughter asked if rehab could be organised to help him stay off the area.
But notes over several months showed the wound was getting larger and deeper, was smelly and oozing, and that the man was frequently in pain.
He had been to the emergency department with urinary tract and kidney infections, and swollen legs.
The commission found care was not escalated fast enough and more than five months after the wound was first noted, he was finally referred to have it surgically cleaned.
The surgeon found Mr A had sepsis, necrosis and a bone infection that meant parts of the sacral bone "came away easily under pressure," the report said.
His family was told Mr A was now likely palliative and he died shortly afterwards in hospital.
The commission found the rest home consistently failed to address the seriousness of the wounds, failed to escalate to a doctor sooner, failed to communicate well enough with his family and should have had Mr A in hospital level resthome care.
Heritage Lifecare, which owned Dunblane at the time, told the commission that staff struggled to help or assess Mr A adequately with his wounds because he was often aggressive towards them.
But the notes did not reflect that, the commission said.
There were only three times in the 26 wound care notes that said he was aggressive or abusive, and the rest of the time he was described as co-operative and pleasant.
Heritage also said Mr A's overall condition was deteriorating and, coincidentally, the pressure wounds deteriorated at the same time.
It responded to criticism that it took too long to contact a doctor, by saying referring him to a wound care nurse specialist would be of more value - and it was that nurse who ultimately referred him for surgery.
The commission recommended Dunblane Lifecare review training for staff in several areas.
The home has been sold since the incident and the new owners, New Zealand Aged Care Services, told the commission it now operated under different management, leadership, policies, processes and nursing staff.
It questioned whether it needed to follow the recommendations but the Commission said it still should.
It also said the commission's investigation should have included the care Mr A had in hospital.
RNZ has also approached the new owners and Heritage Lifecare for further comment.
