Best-fitting models retrieved for J0835, J0501, and J0500 (top to bottom). The upper three panels show the observational flux in black, and the best-fitting model spectra for the three BDs (J0835, J0501, and J0500). The observed flux is normalised to the mean flux of each order–detector pair after telluric correction. The lower panel shows the residuals between the observed and model spectra. The data and the models are displayed in the rest frame of each object. The shaded region at the top of the image indicates the wavelength coverage of the three detectors for each spectral order (CRIRES+ and K2166 wavelength setting). They slightly differ in the rest-frame of the BDs as presented by the gradient. The sixth order (2321.6-2369.6 nm) is shown because it contains several ¹²CO and ¹³CO lines. The data and best-fitting models of the remaining orders can be found in Appendix B.