I'm not sure about Germany, but South Korea was and is extremely effective at testing their population. They also did and are doing a fantastic job tracing infections (although part of this is due to being able to mostly focus on a single super-spreader rather than many simultaneous outbreaks. I think that South Korea probably confirmed 70-80% of their actual number of cases, while Italy probably has at least 2-3 actual cases for each confirmed case. Testing and tracing en masse is really, really hard, and is basically impossible if you don't catch it soon enough. I think that hospital overloading is definitely able to double or triple the death rate, though.