The RT-PCR test can tell whether there is SARS-CoV-2 genetic material at the collection site (typically the nasal cavity).
A random selection of positive specimens are sent for complete genetic sequencing. That’s where the specific variants are determined. It’s the same process used for Influenza each year. It’s how we know which strains to include in the flu shot.
A 'royal' we or are you in on this 'we'? Come on tells US who you actually represent ... sure is a ruse to pretend it is 2a cause.