The COVID moonshot data includes some repeated experiments. The fluorescence assay data include 9 independent CRCs for inhibition of MPro by a compound with database identifier CVD-0002707. The mass spectroscopy assay data include 25 independent CRCs for ebselen. The parameters estimated by applying 4PL versus 4PL+C are shown in Figure of Supporting Information 1. In this figure, we compared 4PL+C to 4PL instead of 3PLFB because the former is more standard and more widely used. For both datasets, 4PL+C reduces the standard deviation of estimated R b and R t compared to 4PL (Table of Supporting Information 1). There was not a statistically significant difference between the standard deviation of pIC 50 and the Hill slope. These results are inconclusive but consistent with the trends observed in the simulated data.