Appreciate this deep dive. Worth adding that there is a detectable bit of extra mortality and morbidity with fingertip pulse oximeters when testing darker-skinned folks. The devices usually face the same issue as smartwatches. This interferes with timely treatment for acute and chronic symptoms of COVID and other conditions which cause lowered blood oxygen concentrations.
Supposedly the tech was out there to solve it, but it was expensive enough that medtech manufacturers hadn’t ever bothered making compatible devices at a scale to serve most patients or consumers.