Suppose that person A has tested positive for Covid19 and visited a restaurant the day before symptoms developed.
The restaurant has a list of people who went in on that day but no record of their arrival/departure times.
Are test and trace going to contact everyone on that list and ask them to self isolate?
What if person B went in just after opening and was the only customer there?
What if person C went in later (and may or may not have been there at the same time as person A) but did not go within two metres of another customer?