Fits of the r light curves of our SNe Ic-BL with the stretched light curve of SN 1998bw (black solid line). This fitting aims at determining the explosion epoch, marked by a vertical magenta line. The pre-explosion limits, marked by empty (g-band) and filled (r-band) triangles, are in agreement with the computed explosion epochs, except in four cases where we instead adopt the last nondetection as the explosion epoch and a value from the literature for iPTF16asu (magenta dashed lines). For iPTF13bxl, we adopt the time of the detected GRB as the explosion epoch (blue vertical line).