Results of the tests of the injection of mock GCs. Top left: Completeness of the HST data when simultaneously detecting the injected GCs in the three HST bands (blue line) and for the OSIRIS+ u-band (purple line). Bottom left: photometric errors for all the bands used in characterising the GCs of MATLAS-2019. Top right: ellipticity errors in the WFC3/F606W, where the ellipticity is measured. Bottom right: R_e errors in the WFC3/F606W, converted to pc assuming a distance of 20.7 Mpc. The dashed vertical lines indicates when the detections fall below 90%.