coin flip accuracy
The CDC itself recently stated in the following document Page 42.
The analytical sensitivity of the rRT-PCR assays contained in the CDC 2019 Novel Coronavirus (2019- nCoV) Real-Time RT-PCR Diagnostic Panel were determined in Limit of Detection studies. Since no quantified virus isolates of the 2019-nCoV were available for CDC use at the time the test was developed and this study conducted, assays designed for detection of the 2019-nCoV RNA were tested with characterized stocks of in vitro transcribed full length RNA (N gene; GenBank accession: MN908947.2) of known titer (RNA copies/µL) spiked into a diluent consisting of a suspension of human A549 cells and viral transport medium (VTM) to mimic clinical specimen
Ie. we don't have a copy of the virus, so we used one from the warehouse that we think is similar as they are "also coronaviruses".
Questions are being asked, by the right people
Higher C q values (above 38 cycles) mean lower amounts of your target nucleic acid. High C q values can also indicate problems with the target or the PCR set-up, as outlined later in the pitfalls section of this article. Your PCR instrument will collect fluorescence data during each cycle.