Families of those who have died have demanded answers
Spot-checks by the health regulator found that 60% of inspected hospitals in England were not accurately assessing their own performance.
A BBC Panorama investigation has found that Stafford was among the hospitals that gave inaccurate information to the Care Quality Commission (CQC).
Last year, the commission scrutinised about one fifth of England's 146 acute hospital trusts.
The government said the way hospitals are monitored is being changed.
Checks by the CQC found that Peterborough Hospital Trust had misreported its performance in three out of the four core areas inspected by the commission, out of a total of 44 areas where certification is required.
Peterborough Trust was deemed a 'fair' hospital by the NHS regulator.
Medical intelligence company Dr Foster publishes its his own league table of patient safety in English hospitals based in part on death rates.
It was the Dr Foster findings that first signalled a serious problem in patient care at Stafford Hospital, which last week was the subject of a scathing report that included evidence of record fabrications and patient suffering and neglect - while for most of that time being rated as a 'fair' hospital by the NHS.
That report followed an earlier report by the CQC's predecessor - the Healthcare Commission - that said patients had been 'dying needlessly' and put the number of excess deaths at more than 400 between 2005 and 2008.
HOSPITAL INSPECTION FAILURES
Of the self-assessment, Professor Brian Jarman, who calculates mortality rates (the difference between expected and actual death rates) for the Dr Foster league table, said patients do not know that those 'good' or even 'fair' ratings enjoyed by their local hospitals are based on the hospital's take on its own performance.
"My view is that patients do not realise that hospitals are self-assessing. I could hardly believe it until I read it."
Prof Jarman said, in the case of Stafford, what struck him even more was that a hospital that he had been flagging for years because of high death rates, was still being listed by the NHS as a 'fair' facility.
He questioned the information about hospitals offered in the regulators' official ratings.
"I really could hardly believe that they would say and publish that hospitals are good when we're saying that there are very, very bad and had been for 10 years."
Health Minister Mike O'Brien said the way hospitals are rated and monitored is being changed.
"It was flawed and that's why we have changed it. And that is why we are now in a position where we don't rely on self-assessment
it is subject to a whole series of checks."
But Panorama understands that self-assessment will still play an important role in the revised system and will still be subject to checks and inspections.
The results of the CQC inspections for 28 hospitals in 2009 show that when just 4 of the 44 'core standards' were double-checked, they found the following:
• Nine hospitals got their self-assessment wrong on one of the four
• Another six were lacking in two out of the four standards
• In two instances, trusts failed in three of the four standards checked
One of those was Peterborough hospital.
The chief executive, Nik Patten, said the hospital's shortcomings were in documenting its work, not in the quality of care and that those issues have highlighted by the inspection have been addressed.
"What it has proven is that our evidence in collecting that paper evidence of quality of services hadn't been as good as it should have been, we've been putting that right now."
Health Minister Mike O'Brien said the health service is much less secretive about local hospital performance than it has been in the past, but, he added, there is room for improvement.
"Is it open enough? No, it's not open enough. And we need to be much more open in the future than we have been in the past."
Panorama: Trust Us, We're an NHS Hospital, BBC One, Monday, 8 March at 2030GMT.