Initially, no one knew which students were involved so all 31,000 teenagers had to verify their results at their respective schools.
The Northern Ireland Council for the Curriculum, Examinations and Assessment (NICCEA) said it has since introduced checks and balances to ensure the error will never happen again.
It was the third embarrassing exams failure in the province inside a year. First, 18,000 children had to sit a third 11-plus paper when questions were leaked. Then two physics papers based on separate syllabuses contained some identical questions but were timetabled for different dates.
A document outlining the measures taken to revamp the examinations system is likely to be published in the near future. But council officials said it was not the result of the mistakes. "It is something we always wanted to look at," a spokesman said.
In the GCSE blunder, one box of 6,000 pre-printed slips which omitted the heading for Child Development was used by mistake during printing. Consequently, results for a number of subjects were displaced by one column. On the remaining slips, grades were wrongly interchanged with Child Development and Business Studies.
In letters to school principals, NICCEA accepted that its control procedures were inadequate. New quality procedures and audit trials have now been put in place and a review conducted into its information systems and processing.
The council indicated it was up to education minister Michael Ancram to decide whether to publish its report, but he appears to have written back leaving the decision to NICCEA.
The council argued that it would be unfair to individuals and it was not normal practice to issue such reports.
However, a spokesman said: "It was a really serious mistake and extremely embarrassing from our point of view. But it was human error. We carried out a very detailed investigation and took the measures necessary."