Comparison of the models presented in Chacón-Tanarro et al. (2019) – S16 (obtained with pyRate) and V17 (obtained with MONACO) – to the 1D-4 model (fiducial model) computed with an updated version of pyRate. The column density profiles are shown at different time steps: t = 1.6 × 10⁵ yr for V17, t = 3.0 × 10⁴ yr and t = 3.0 × 10⁵ yr for S16, and t = 3.0 × 10⁵ yr for 1D-4. The observed profiles are depicted in black (errors as grey-shaded areas). The CO column densities were obtained using observations of C¹⁷O and the average isotopic ratios of ¹⁶O/¹⁸O = 557 and ¹⁸O/¹⁷O = 3.6 in the local interstellar medium (Wilson et al. 1999).