Extension of the Na-O anti-correlation as given by the empirically calibrated IQR2[O/Na] values from Carretta (2019) as a function of total absolute magnitude M_V from Harris (1996, 2010 online edition; left panel) and of the present-day and original total GC masses (middle and right panels, respectively) from Baumgardt et al. (2018). GCs with robust detection of changes in Ca (K and Sc) in the present census are indicated with filled red circles.