Checks on stars with dubious membership. Upper panel: radial velocity profile of NGC 6388 based on our sample. The RV refers to the cluster systemic velocity of 82.5 km s⁻¹. The open circles indicate stars defined as non-members in APOGEE DR17. The vertical lines indicate the half-mass and tidal radii from Harris (2010). The dashed lines show the ±3σ velocity dispersion profile of the best-fit King model as in Lanzoni et al. (2013). All 185 stars fall well inside its limits. Lower panel: for stars in common with APOGEE DR17 and considered non-members there, we show the offsets from the cluster mean elemental ratios ([el/Fe]). For each element, the red and blue lines indicate the 1σ and 3σ limits, respectively. Only the Ba value for star l63p075 is off by more than 3σ, and we conservatively excluded this abundance from the computed average in Table 1.