When trying to compare the COVID-19 with previous disasters or crashes, the closest comparison we can find is that of the oil spill on the BP platform in the Gulf of Mexico in April 2010. In both cases the scale of the disaster was unclear for a long time. In addition to that, the S&P index fluctuated wildly with many local minima that could have been mistaken for the bottom. It is likely that many investors miscalculated and purchased as many assets as possible during that false bottom before the real one was reached.
With the oil spill, the crash did not happen until May 2010, and lasted until early June with several brief recoveries. By the end of the crash the index fell by 17 per cent. The index began to recover in earnest afterwards, even though the oil spill itself continued until September.