Also, PCR is not one test, one method, one process. There are hundreds of distinct PCR-type molecular nucleic amplification tests. CDC guidance would only apply

Also, PCR is not one test, one method, one process. There are hundreds of distinct PCR-type molecular nucleic amplification tests. CDC guidance would only apply to the one process they provide/support. For a survey of the ecosystem and the difficulties in standardizing Ct values, see e.g. https://www.aacc.org/science-and-research/covid-19-resources/statements-on-covid-19-testing/aacc-recommendation-for-reporting-sars-cov-2-cycle-threshold-ct-values https://www.aacc.org/science-and-research/covid-19-resources...