Top: Number of galaxies in the comoving error volume of BNS detected by ET alone (top panel) and in a network with CE (middle panel). Each point corresponds to one GW BNS detection. Different colors correspond to different magnitude intervals. The black dashed line represents the number of WST fibres. Bottom: Probability distribution function of the number of galaxies with apparent I-band magnitude m < 25 that can be found in the comoving error volume of each BNS detected by ET + CE, for different redshift intervals. Dashed vertical lines indicate the mean value around which each Gaussian is centred.