Final MUSE spectra for the three quadruply imaged AGN systems. For each system, the four AGN images are shown in different colors, following the same color-coding adopted in Fig. 3. The top row shows the first two quadruple systems, while the bottom-left panel shows the four AGN spectra of J0957. All spectra are corrected for Galactic extinction, normalized to Gaia photometry, and shifted to the rest frame. Vertical blue dashed lines mark the wavelengths of the main emission lines. Since J0957 data also allowed us to identify the foreground lensing galaxy, its spectrum (component E) is shown separately in red in the bottom-right panel. For reference, the AGN spectrum that contaminates the lens is shown in gray, while the emission lines of the lensing galaxy are indicated by black vertical dotted lines.