Excess Δ(log(N/O)) of N/O with respect to the local N/O–O/H relation from Vila-Costas & Edmunds (1993) as a function of redshift for galaxies with abundances from the direct method and N/O from rest-optical lines. Low-z star-forming galaxies and H II regions, LzLCS and LyC22 samples are shown with the same symbols as in Fig. 4. Other N/O measurements from the rest-optical lines, obtained primarily from JWST spectra, are shown at z ∼ 2.2 (red symbols, from Sanders et al. 2023), for the EXCELS sample (green stars; Arellano-Córdova et al. 2025a; Scholte et al. 2025), from Stiavelli et al. (2025, magenta), the Sunburst arc at z = 2.4 (orange; Welch et al. 2025), and for the z = 6.1 lensed galaxy (orange) from Topping et al. (2024), with measurements from rest-optical lines by Berg et al. (2025). The two orange symbols indicate objects known to also show UV-emission lines of nitrogen.