1) Tos. says the bas kol is for the zachor.
2) Bas ploni doesn’t identify the girl, just her father.
3) Some rishonim say that zivug rishon/zivug sheini doesn’t mean first marriage/second marriage, so many people might not be marrying their zivug rishon, and therefore not the person mentioned in the bas kol.
The bottom line is as apy says; do normal hishtadlus but have bitachon in Hashem.