Frank Corbett said he thought the budget had been printed off before the error was spotted. (CBC)

The leader of the Nova Scotia Progressive Conservatives says the NDP government has lost its credibility by trying to cover-up a mistake it made in last year's provincial budget.

The budget deficit should have been $27 million more than forecast.

Jamie Baillie said the error was an honest one, but the government chose not to correct it.

The Progressive Conservatives used freedom of information legislation to show budget documents were sent to the printer more than a week after the Finance Department confirmed its figures were off by $27 million.

The Auditor General had flagged the discrepancy two weeks prior to that and the Treasury Board knew about the error at least three days before printers began to roll.

Last month Treasury Board chair Frank Corbett defended the decision not to correct the mistake saying there wasn't enough time. He said he thought the budget had been printed off before the error was spotted.

"A cut-off date is decided for every budget and it had been reached … the documents had been sent off," he said.

Corbett was unable to recall the actual cut-off date or final deadline to send budget material to the printer.

The budget address delivered by the finance minister was printed on April 2, the day before the budget.

Baillie said information from the printer suggests otherwise.

"The NDP had lots of time to fix the mistake in the budget and to tell Nova Scotians that the budget contained a mistake, but instead of fessing it up they chose to cover it up and I believe that is a big problem," he said.

The finance minister has said a $27 million projection in a $9.5-billion budget wouldn’t have made any difference.

"We updated the error when we should have and that was at the quarterly update," said Corbett.

"You are asking me about the value of hindsight."

Baillie said it's not about the numbers but whether taxpayers can trust the government when it promises to bring in a balanced budget this April.

"Now that we know we had a false budget last year, how can we have any faith in the budget that’s coming forward this time?" he asked.

Corbett said on Thursday that he assumed a printing deadline had passed and changes were not possible.

Premier Darrell Dexter said he did not know about the budget error.