Correlation coefficients derived by choosing values from different spectra of the individual star and computing the correlation of to log(L_X/L_bol) for all stars 1000 times. Top: considering the valid sample and all available TIGRE spectra (blue), or only the pseudo-simultaneous data (green). Bottom: same as above, but for the 88 stars with TIGRE data older than 750 days before the start of the eROSITA observations. Choosing data only from these old data leads to a poorer correlation (red). For both panels, the vertical dashed black line represents the correlation coefficient obtained with the median value of of all available data for the valid sample. The vertical solid black line represents the same using pseudo-simultaneous data.