How much knowledge though do you think a young boy with a year or two's training actually has? Sometimes the indicator of a place that just turns out black belts is giving them to young children. There's many places that advertise you will get a black belt in a year if you train with them, how much knowledge do you think those 'black belts' will have even if they have it in them to be good martial artists they have been cheated out of their knowledge.
And... that would be why rank only has meaning within the school/system that awarded it.
In schools that award a 1st Dan in a year, it's clear that most people can gain the knowledge and skill required for a 1st Dan IN THAT SCHOOL in one year. In other schools, that time frame is totally out of the question.