To share some insights, started as Geo 2 officer.

Year 1 C
Year 2 Promoted to Geo 3 (D)
Year 3 C
Year 4 C
Year 5 C
Year 6 Promoted to Geo 4 (C)

I did something wrong in year 2. To be honest, it all depends on your school. So the C-, D meant no promotion for next 3 years, it's true.