ETL is free to map to all the variety of specific LOINC / SNOMED tests
Absolutely not ! This is an antithesis of COMMON data model. The goal of ELT guidance for sites with COVID data is precisely to make the world unite on some useful conventions. It is OK to have broad definitions (for the sake of good study), but accompanied by some “preferred” ETL recomendations for week 4 and months 2 and 3 of the epidemic.
Phenotype studyathon subgroup is planing to mention those preferred options. See this thread here