Fraction of systems that satisfy the 3σ variability criterion (Eq. (2)) as a function of the ΔRV_min variability criterion for the entire sample (black solid line) and for probable RSGs (red dashed line; as defined in B19). This figure highlights that the majority of the sample do not satisfy the 3σ variability criterion and that the maximum observed binary fraction is ∼0.30. Only one target in the sample (VFTS 744) displays significant variability above ΔRV_min = 7.0 km s⁻¹.