The BBC is explaining missing cases like this:
UK's 16,000 missing cases 'caused by file size issue'
For the last two days, the UK has seen extraordinarily high daily recorded figures for confirmed coronavirus cases as Public Health England scrambled to catch up with 15,841 infections which should have been reported last week.
But how did the delay occur?
The technical issue to blame was a problem with the maximum file size permitted on the system, according to the PA Media news agency.
Some files containing positive test results were too large for the system that takes in the results and loads them into central systems, officials told the agency.
They said that rapid measures have been taken to ensure the issue does not happen again.
Either the system has astonishingly low file size limits - or the files are astonishingly large! Even ordinary WIndows 10 has a Maximum file size: 256 terabytes. (Far more likely to hit hardware limits!)
In either case, clearly not tested. Just like most of the population.