The 44-year-old mother of three first injured her lower back in a trampoline accident and her family doctor's note send to ACC referred to spondylolisthesis, which was shown in an X-ray.
However, ACC could not find a record of that claim but Halvorson had kept her medical notes and X-ray results that formed part of her appeal lodged in the District Court early last year.
The claim was not pursued then because her parents used their medical insurance to pay for treatment, including three surgeries.
Halvorson said her back settled down and she was able to live an active life for about 22 years, until she injured it again in 2014 while moving furniture.
Her advocate Jeannette Brock told the court ACC was not prejudiced at all because it held a completed referral form from the GP who attended to Halvorson within 24 hours of her trampoline accident.
Brock said ACC's own specialist John Ferguson, a spinal surgeon, who concluded the trampoline injury gave rise to her subsequent spinal issues.
The court agreed with that conclusion.
"She's so de-conditioned and I don't think she'll ever get back to work. Her husband has had to give up work to look after her and they've had to take boarders to supplement their income," Brock said.
Halvorson has struggled just to function at a basic level and could not afford physiotherapy while waiting for cover.
She said the culture at ACC has still not changed and that one third of her clients with work-related injuries were not getting weekly compensation.
"I am dealing with 104 ACC reviews and have filed 11 appeal applications so far this year. In this case, we gave ACC a chance to settle before taking it to appeal which we knew we had a good chance to succeed."
An ACC spokeswoman said it would uphold the court's decision and would not appeal the ruling.
"We are working with Ms Halvorson to calculate her complex entitlements," she said.