Left: encounter rate (Γ_d) as a function of lookback time for young stars formed in an e_d = 0.7 disk steadily over the past 150–500 Myr. Right: Production rate of HVSs from an e_d = 0.7 disk via gravitational slingshot by an SMBH–IMBH binary, which has a mass ratio of 5 × 10⁻³ and evolves from a semimajor axis a_MBHB ≃ 160 au at 500 Myr ago to the final coalescence at ≃10 Myr ago mainly driven by gravitational wave radiation. The dashed purple curve shows the HVS production rate obtained from the empirical model in C. Cao et al. (2025), which assumes an analytical encounter rate that decreases exponentially after 150 Myr ago. The cyan shadow region indicates the lookback time of 50–250 Myr when the late B-type HVSs in the halo were ejected.