Listed on the Frankfurt stock exchange, the British team this week revealed a pre-tax loss of almost $8 million last year, having turned a profit in 2011.
But spokesman James Francis said the financial report could not include almost $15 million in Formula One income.
"If that figure had been included we would have turned a loss into a profit," he told the Oxford Mail.
"It would have been a smaller profit (than 2011), but a lot of investment has happened."
The Williams spokesman said building work on a new research and development department is still scheduled to start.
The team is yet to score a point in 2013.
"There is still a way to go for the team to get to where we should be," said Sir Frank Williams, "but improvements on previous seasons are evident."