Simplified... There is no such thing as promotion. Every job is posted, and every dxo goes through the same interview as an outsider but 1. Gets priority 2.gets preference. At least this is what HR suggest.

Actually HR is super unclear about this. A job can be dx9-11. Does this mean if your boss thinks you are good, starting from dx9 there is no need for interview for the next 5 years? Assume 2 years, 2x C+ to jump 1 grade.