I wouldn't put much faith in an accountant if he miscalculated and made me overpay 41.8% in taxes. He would quickly be out of business if he brushed aside every mistake that was that large saying it was a minor point.
With the left always overstating $50B more than the actual as you state it does a tremendous disservice perpetuating and enabling the lie.
The Conservative's GDP growth during the recession wasn't as bad as you make it. Canada was the economic darling during the recession showing growth that almost all other countries could only wish for considering the global stagnation.