The so-called Kosen Judo rules differed from Kodokan Judo rules in that matches were allowed to continue in ne-waza even if no progress in technique was evident, but the techniques used are the same. Also, there was the so-called "Kosen Rule" that permitted you to enter directly into newaza without first applying tachiwaza. In other words, they explicitly permitted "drag-downs" as well as tactics like walking into the centre of the mat and sitting or lying down, before coming to grips. This was the rule that Kano later changed.
Kosen is actually a contraction of:
Koutogakko 高等学校 = High School
PLUS
Senmongakko 専門学校 = Technical or Professional College
EQUALS
Koutosenmongakko 高等専門学校 = High Schools & Universities i.e. "Scholastic," in this case referring to what we might label an Interscholastic Judo League.