Residual between the observed flux and the light-curve model in Goobar et al. (2017), Dhawan et al. (2020), Johansson et al. (2021), Mörtsell et al. (2020). The x-axis shows the days since the maximum of the light curve. Only a subset of the entire data set is shown. HST data (F814W and F625W) is available only ≈30 days after the maximum. Prior to this date, the observations cannot resolve the four individual images so the residual corresponds to the sum of all four images. The dashed line marks the adopted ±0.1 mag upper limit, for the allowed range of variability in the light curves.