The exams watchdog first identified a major problem at the heart of this summer's GCSE grading crisis almost three years ago - but failed to act, reports say.
Ofqual highlighted concerns that modular GCSEs - qualifications split into bite-sized chunks - created risks in maintaining standards from year to year because they allowed pupils to "bank" grades early.
It came up with a workable solution that might have avoided the marking row that erupted last week, but decided not to implement it, the Times Educational Supplement (TES) said.
The disclosure came on the day that Ofqual prepared to publish interim findings of its investigation into a steep decline in the number of students awarded good GCSE grades this summer.
Figures show the percentage of pupils gaining A* to C grades across all subjects fell for the first time in the exam’s 24-year history.
National GCSE results for all subjects in England, Wales and Northern Ireland revealed 69.4% of exams were given at least a C grade - down 0.4% on last summer.
Particular concerns were raised about English, where 63.9% of pupils gained at least a C, compared with 65.4% a year earlier - a 1.5% drop.
Angry headteachers claimed exam boards had raised grade boundaries in English halfway through the year amid fears too many children were going to get a C.
Ofqual has admitted there are questions about how grade boundaries were set in a small number of English units over the year.
The TES reported that former Ofqual chief regulator, Isabel Nisbet, raised the problem in October 2009 when modular GCSEs were first introduced.
She identified problems maintaining standards in a system allowing pupils to bank results half way through the year.
She proposed scrapping banking grades in case their result later proved to be too lenient or too harsh.
An Ofqual spokesman said: "The idea was put forward for discussion by the wider education community and was not a formal proposal."
Elsewhere, an education think-tank has warned that a sharp drop in students applying to train as primary school teachers could lead to a crisis in the classroom.
Applications for graduate and postgraduate primary teacher training courses were 17% lower this year than last, partially due to an increase in tuition fees, a report by Professor John Howson for the Pearson Think Tank said.
He found that low morale in the profession and rapidly rising pupil numbers were creating the "perfect storm" which could culminate in major problems recruiting enough staff in the future.
