The PCR test that hospitals have been using is qualitative PCR, meaning end point. It is not as accurate as real time PCR.

In the context of viral infections, the difference between the endpoint and RT-PCR is the following: Endpoint PCR will let you know if the virus present or absent even if there is a few copies of the virus after 30 cycles PCR will produce the signal, 2^29 is a huge amplification power if you have single virus sequence after 30 cycles you will get 536,870,912 copies.

If you run RT-PCR for the virus you can determine the viral load.

This is why asymptomatic patients test positive.