different instructors will have different criteria, some solely use competition results, others will use a combination of the methods you list above. Some organisations will only allow the head instructors to promote even if the academy instructor is a black belt. It's one of the unique things about BJJ, unlike other martial arts there is no set criteria written in stone.
You even have people graded by TAM, Blarney Stone or HBOS
Scotlands No. 1 Timekeeper also available as a BJJ/No Gi referee