People being tested for coronavirus in England were not asked to provide addresses for weeks during the height of the pandemic, it has emerged.
The BBC understands Public Health England is now trying to match addresses to positive test results to understand the spread of the virus.
Councils say some of the case data they receive is "poor and incomplete".
The government said councils now have the ability to access data down to the "individual and postcode" level.
But Labour's shadow health secretary, Jonathan Ashworth, said the mistake "simply beggars belief".
Health Secretary Matt Hancock set a target to carry out 100,000 tests a day on 2 April.
But the Department of Health and Social Care has confirmed users of the service only had to provide their postcode from 23 April.
Councils and local directors of public health told the BBC they had been asking the government for months for access to data about the number and growth of cases in their areas.
Public Health England began sharing test data - including postcodes - on 24 June, after councils began signing data-sharing agreements.
As the national lockdown eases further, Prime Minister Boris Johnson has spoken of a "whack-a-mole" approach to combat outbreaks on a local level.
It led to a local lockdown being implemented in Leicester, after a spike in cases across the city.
One director of public health, who asked to remain anonymous, told the BBC not having reliable geographic data about cases locally meant they were using "a mallet the size of a district - you take out a lot more than a mole".