Postal votes from the 2004 Birmingham city council elections, discovered hidden in a box ten months after they should have been counted, could have changed the result in two wards.
Analysis of 175 packets containing 255 votes has shown it is possible that two candidates who narrowly lost in Kings Norton and Longbridge might have been elected had the missing votes been counted.
But it is impossible to be certain, since legal restrictions prevent officials from inspecting ballot papers so long after the count.
Although the Birmingham returning officer, Lin Homer, knows how many votes in the box came from each of the city's 40 wards, she does not know in whose favour the ballot papers were filled in.
The uncounted votes could not have changed the political balance of the council.
In Kings Norton, the gap between elected candidate Margaret Sparrey and the runner-up Tony Ward was one vote. Both are Conservatives.
In Longbridge, the gap between elected candidate William Green and runner-up Fiona Saxon was nine votes. Both are Labour.
City elections officer John Owen and another member of staff were suspended from duty following the discovery of the box two weeks ago. An internal council inquiry is under way and the box is in the hands of the West Midlands Police economic crime unit.
Mrs Homer has taken the unprecedented step of writing to all 477 candidates who stood in the 2004 council elections.
She said in her letter: "The advice I have received is that because the time prescribed the Representation of the People Act 1983 for challenging the result of an election has passed, even if the votes could have affected the outcome of the election in your ward, it would still not be possible to displace the declared results of the 2004 election."
Her explanation did not convince deputy council leader John Hemming, who discovered the uncounted votes locked in a cupboard in the elections office.
Coun Hemming (Lib Dem South Yardley) said: "I think she could examine them if she really wanted to. She should count the votes if for no other reason than to stop people griping about what happened."
Yesterday it emerged that West Midlands Police will visit the homes of postal voters in the region to ensure they are genuine.