Synthetic spectra of HNC and isotopologues obtained with LOC (top rows: L1544, bottom row: HH211). For L1544, the results are splitted between using the Keto-Caselli model (top) and the HDCRT model (centre) as approximation for the physical structure of the core. Towards L1544, the best-fitting abundances and timesteps are 2 × 10⁻⁸ (KC), 1e5 yr (STKC), 5 × 10⁻⁸ (HD), 1e5 yr (STHD) for HNC; 2 × 10⁻¹⁰ (KC), 1.3e5 yr (STKC), 2 × 10⁻¹⁰ (HD), 9.8e5 yr (STHD) for HN¹³C; 3 × 10⁻⁹ (KC), 1e5 yr (STKC), 8 × 10⁻¹⁰ (HD), 9.8e5 yr (STHD) for DNC. Towards HH211, the best-fitting abundances and timesteps are 5 × 10⁻¹⁰ (const), 1e5 yr (2-phase) for HNC 1 × 10⁻¹¹ (const), 1e5 yr (2-phase) for HN¹³C; 7 × 10⁻¹¹ (const), 1e6 yr (2-phase) for DNC.