P-P plots for GRB afterglow injections. Each panel shows a P-P plot for the recovery of the parameter displayed in its top left corner. The P-P plots show the cumulative distribution of the injected values’ posterior quantiles for 200 injections. The lightblue curves indicate injection recoveries with AFTERGLOWPY, the magenta ones for PYBLASTAFTER-GLOW. The solid lines signify that the injections stem from physical base model, the dashed lines indicate an injection with the surrogate itself. The gray areas mark the 68-95-99.7% confidence range in which the quantile distribution should fall if it was uniformly distributed.