I have read that in Japan there was a general system called jujitsu. However there were hundreds of branches of jujitsu. Most samurai were trained in different branches of jujitsu. Basically any martial artist in Japan had some form of jujitsu training. It was even implemented into some karate-do. They did not specify it as jujitsu inside karate-do.
Anyway I read Kano himself had licences to teach various branches of jujitsu which he later combined and removed the deadly techniques from in order to train at full speed and power. He called this Judo. This license system was before the belt system was created by Kano himself for Judo. No system had a belt ranking before Judo. I think Kano had about five styles he used techniques from. Anyone else heard of this or can confirm about Kano's training before he implemented judo in Japan?
Tenjin Shinyo Ryu under Hachinosuke Fukuda and Masatomo Iso
Kito Ryu under Tsunetoshi Iikubo
the Kito style was very different from the Tenjin Shinyo style jujutsu to which I had by then become well-accustomed. In Tenjin Shinyo, there are a range of strangulation techniques and groundwork hold-downs. On the other hand, the Kito style, rather than hold-downs, comprises a wide range of effective throwing techniques. There are a number of sacrifice throws together with several foot and several hip throws I had never seen before.
To complement mattm's answer, Kano elaborates slightly on the other schools he may have studied in another quote:
I first studied Tenjin Shinyo-ryu jujutsu With Fukuda Hachinosuke. After his death, I continued my studies with Iso Masatomo in the same school ofj ujutsu, and after his death I learned Kito-ryu from Iikubo Tsunetoshi. I subsequently studied all the other schools.