Star keeps changing its premiere stategy every year.
2017: Premiere on Star Gold and Star Gold Select simultaneously. This was the only year in which Star Gold Select was given any importance for premieres, because it was a new channel launched in 2017.
2018 (after the Rishta Wahi Baat Nayi rebrand of Star Plus in May): Premiere on Star Plus first and Star Gold later (e.g., Baaghi 2, Sanju, Stree). But Badhaai Ho was premiered on Star Gold first.
2019: Premiere on Star Plus and Star Gold simultaneously (e.g., the films you mentioned).
2020: Some films are premiered on Star Gold (Bala, War, Angrezi Medium), others on Star Plus (Love Aaj Kal, Mardaani 2, Tanhaji).
In fact, Star Gold 2 was supposed to premiere movies along with Star Gold, but this happened only for Bala and not thereafter.
Among pay GECs Star Plus has the highest viewership by a large margin. Sony Sab is way behind.