For promotion beyond GEO3, you need to show potential to perform at the next level. safest bet is you need consistent and upward performance trend of at least 3 years. Based on this and previous year C+ And the year before C, it could be next year promotion if your CEP is high. Otherwise you need another C+ for next year to continue the upward trend. More importantly, you need to stay consistent in your grade.

Hope the above helps.