The question is if you are an Honor Noble Baron. That is without any position in the government, but Baron none the less. And now you are asked to join e.g. the Ministry of Defense in a position requiring your title as Baron. Are you still an Honor Noble, or have you become a Rank Noble? As the text says you, as Baron, would be considered over any lesser rank or commoner assuming a minimal level competence.I may be wrong, but I'm fairly sure that rank nobles were described as those few commoners who needed a title (because of the rule that certain governmental positions required the holder to have a given noble title as a minimum). The point of a rank title is that it's given to a commoner and that it's usually a life title.
It seems to me that ceremonial titles are not quite the same as rank titles. There would be no need to give an honor noble a rank title unless he was appointed to a position that required a greater noble rank than his own and that would be quite rare.
My reading of that text is there may be a fair number of conversions from Honor to Rank nobles, without too many promotions. Over the centuries, you don't need too many promotions
And neither much discuss the process of going the other direction. That is, the child which inherits a title, but not the position in government. If they never take the position, does this mean they've become Honor nobles?
If either or both are true it means the distinction between Honor and Rank, at least for subsequent generations is not a strict one.