Those numbers are correct for each of the 4 years. The average could include Perkins loans which not everyone gets. Also, if a parent applies for a Parent Plus and is denied, the student can get $4k extra in unsub loans I believe. That’s the independent student amounts which could be raising the averages. The averages could also include private loans in the student’s name but cosigned by parents or others.
For sub loans the government pays the interest while the student is in school, unsub accrues interest while the student is in school.
I also think those averages may be for those that have any debt and not include those who graduate debt free by attending affordable schools.