More than 13,000 people rejected for disability benefits after receiving "zero points" on their assessments were later awarded payments, new figure show.
Campaigners warned the assessment process for personal independence payments (PIP) is "broken" and has "deep and widespread" failures.
Their concerns emerged after figures released to Parliament showed a total of 66,180 people had an original decision by the Department for Work and Pensions (DWP) overturned in their favour at mandatory reconsideration or by a tribunal in 2016.
Within this data, 8,100 people initially scoring zero points on tests by DWP were later awarded PIP by independent tribunals.
A further 5,030 applicants had their decision overturned at mandatory reconsideration, a system run by DWP that claimants must go through before appealing to tribunals.
DWP says only a fraction of PIP decisions are overturned, with PIP awards based on evidence provided by the claimant and their medical specialist.
But the figures, released in response to a written parliamentary question from Labour's Chris Matheson, come amid growing numbers of people being handed zero scores while record numbers of claimants are having decisions to reject them for PIP overruled.
Mr Matheson, City of Chester MP, told the Press Association: "So many of my constituents come in here and clearly they have a disability or debilitating illnesses - and that's from someone who's medically qualified - and they're getting knocked back for the most spurious reasons.
"Every time we challenge them - and we go into detail, my staff sit down with these constituents - we can see the guidelines haven't been followed.
"When we challenge, so many cases get overturned or the number of points jumps right up.
"The system is broken and is designed to take money from people whose only crime is to be unlucky, to be born with a genetic problem or to suffer an accident that completely changes their life."
He called for private companies Atos and Capita to stop doing the assessments and for the process to be brought back into the hands of civil servants.
He added: "There has to be an element of compassion.
"If somebody can't be bothered to work then I've got no time for them, but most people that this affects are affected by misfortune."
The number of points an applicant receives in their PIP assessment determines whether they are eligible for either element of PIP and, if so, whether at the standard or higher rate.
For each component of PIP, a claimant needs at least eight points to get the standard rate or 12 points to get the enhanced rate.
Last year the DWP made around 940,000 decisions on PIP, suggesting one in every 14 decisions eventually gets overturned in favour of the claimant.
Around 65% of all cases that reach a tribunal are overturned, compared to 18% reversed of all those at mandatory reconsideration.
Robert Meadowcroft, chief executive of Muscular Dystrophy UK, said: "PIP assessments are poor in quality and today's data shows yet again just how seriously wrong they can be.
"Taken together with the fact that the majority of PIP cases that are appealed are overturned, this is evidently a system with failures that are both deep and widespread.
"Each case represents profound stress and financial uncertainty for a disabled person.
"We need the Government and providers Atos and Capita to raise the standards of assessor training to make sure they are delivering assessments accurately and fairly in order to bring this number down."
A DWP spokeswoman said: "Since PIP was introduced in 2013, more than two million decisions have been made and of these 7% have been appealed and 3% overturned.
"Assessments are carried out by qualified healthcare professionals, and decisions are based on the evidence provided by the claimant and their medical specialist."