Spectral extraction completeness (S/N >  5) for all clusters with respect to the ACS catalogue as a function of brightness (filters are listed in Table 4). Each grey curve represents a single cluster, the curves for NGC 2808, NGC 3201, and NGC 7078 are highlighted. Since the completeness mainly depends on the stellar density, it also depends on the radial distance to the cluster centre (see Fig. A.1).