Box plot of the resulting central wavelength position from fitting all of the PENELLOPE VLT (ESPRESSO, UVES, X-shooter) and the further HARPS YSO spectra. The boxes extend from the lower to upper quartile values of the data, with a green line at the median. The whiskers extend to 1.5 times the box range. Outliers are indicated by circles. The mean central wavelength position is marked by the dashed magenta line. Positions of the ⁷Li D₁, D₂, and ⁶Li D₂ lines are indicated by the dashed and dash-dotted black lines. The grey shaded area indicates the range of values of the Li I line centres that were used as reference for the RV calculations in previous works.