Errors have been found in the records of around 3,000 former and current civil servants, which affected their starting salaries and medical leave wages, among other things.
Disclosing this yesterday, the Public Service Division (PSD) said it discovered the errors while upgrading the civil service's human resources and payroll IT systems.
The civil service will compensate both current and past officers who were underpaid because of these errors, with the total sum amounting to around $10 million.
Those affected represented about 2 per cent of the civil servant population over the past two decades, said PSD.
It said it took more than two years after the errors were discovered to trace and validate the IT system errors, check 102,000 current and past records which date back to the 1990s, and recalculate benefits.
Most of the errors related to inaccuracies in the full-time national service records of civil servants.
Further checks also found errors in the calculation of medical leave wages, as well as in a program used to compute payments that some pensioners make when they retire from the service.
The mistakes arose primarily because of human error in data entry, as well as the coding of the IT systems involved, PSD said. These systems also had inadequate error detection capabilities, it noted.
PSD said the Government will not be recovering the $3.9 million in excess money paid out, "given that these resulted from errors made a long time ago".
It is also working with all statutory boards to check and verify their employee records. "The statutory boards will similarly make good any errors if discovered."
Mr Loh Khum Yean, permanent secretary in the PSD, said the Public Service is deeply sorry for the errors and inconvenience caused.
"We will make every effort to reach out to every adversely impacted individual to apologise for the error, explain the situation, as well as make good the discrepancy," he said, adding that steps have been taken to ensure such inaccuracies do not recur.
To make up for these errors, those affected may have their pension amounts recalculated or be given a one-time leave difference. They will be paid for long-service awards they missed out on, and the next tier of awards will be brought forward.
PSD said it will also compensate those who had to use no-pay leave due to insufficient sick leave and rectify the shortfall in starting salaries, where applicable.
Asked why it took two years to disclose the errors, a spokesman for the PSD said it had considered whether to start notifying affected officers while it was still verifying the potential impact, or do so later, after it was more certain.
"On balance, we felt it was important to check through the records comprehensively before notifying the individuals in a systematic exercise. This is so that we can better appreciate the extent of the workforce that is materially affected," she said.
"Moreover, the friends or colleagues of individuals who were adversely affected and informed may also wonder if they are affected, and we will be in a better position to address their concerns. Nevertheless, we will be making good the shortfall with interest, to make up for the time lapse."
Explaining how the errors occurred, PSD said the national service period is taken as part of a civil servant's length of service.
However, the "fitness cut" period - where enlistees who meet physical fitness requirements serve one or two months less than their peers - was not included in the records of some 1,400 civil servants. This affected areas such as starting salaries, retirement benefits, leave eligibility, extended sick leave quotas and individuals' eligibility for long-service awards.
Another error involved wrongly using gross monthly salary instead of average monthly earnings to calculate medical leave wages for injured employees on service injury leave. This affected around 1,000 people.
The last error was discovered in the program used to compute payments that some pensioners make when they retire from the service, affecting some 500 people.
PSD will contact all current and former civil servants who were undercompensated owing to the errors by March next year.
People who have left the service will receive a registered letter at their last-known address, as well as phone calls and home visits.
Those with questions can approach the human resources departments of the government agencies they are working in or were employed with.
They can also write in to email@example.com.