It's a principle of Australian democracy that every vote counts - and is counted. But as results continue to trickle in from Saturday's council elections, many voters will be surprised to learn theirs won't necessarily be.

The electoral commission's approach to vote counting is under fresh scrutiny as an expert warns its "buggy" method of sampling and projecting results in favour of counting ballots individually has likely resulted in two recent cases of the wrong person winning positions on NSW councils.

Dr Vanessa Teague says at least four errors have been found in the Electoral Commissions' code. Credit:Tony Zara

While voters' first preferences are counted in full, the NSW Electoral Commission instead calculates voters' later preferences by choosing a random sample of ballots and then extrapolates results using a secret computer code.

"People are seriously shocked when they hear that their votes aren't counted in local elections," said Greens MLC David Shoebridge. "There are a number of tight races with multiple candidates and complicated preference flows where this could make a difference and the wrong person gets elected".