Spectra of the considered sources. Top panels: Redshift-corrected spectra with continuum and iron line fits overlaid. Dotted gray rectangles indicate the regions that are magnified in the lower panels, where detailed line fitting is performed. Bottom panels: Fitted emission lines (e.g., Hβ–[O III]λλ4959,5007 or Mg IIλ2800–[O II]λ3727), along with the corresponding residuals. Continued on the next page.