Top row: stellar abundance ratios [C/Fe] vs. [Fe/H] of the X-shooter catalogue after applying the optimal method, with the original synthetic grid from Knowles et al. (2021) (top left) and with the extended [C/Fe] dimension (top right), with the estimated internal uncertainties as vertical error bars. Each red point and error bar corresponds to the measured [C/Fe] average and scatter in metallicity bins of 0.5 dex. Bottom row: HR diagrams of the final X-shooter stellar sample with reliable [C/Fe] abundance measurements from the extended grid over the whole analysed X-shooter sample in this work (grey crosses, bottom left), and colour-coded by the carbon abundance estimate (grey crosses, bottom right).