We have Ananda group of Students
Maha Kassapa group of Students
And Sariputta group of Students
That’s the favorite Teachers
Obviously there is more Students that each had their favorite teacher.
The available body of Buddhist scriptures was made from the earliest discourses that each had. The discourses are remembered by each group from a different angle. Since it was how the first teacher remembered it. But by the time the discourses was written down these groups became established firmly after more generations. But each kept their own tradition and developed it more and took discourses from each other till it came to it’s final end. The first meeting of sangha was just a confirmation of what each main teacher accepted as Buddha teachings. After that each went to keep being the teacher they always was and teach their students how to memorize the Buddha’s discourses according to how he heard it from Buddha himself or from another monk. If a discourse was directly related to himself we get more detail. In last generation of each lineage things got added during the new development in Buddhist lineages tradition. The last we have of these lineages doesn’t say how each started. It’s all changed already because it became a living organized tradition.
The way discourses are made about other monks or nuns that is not Buddha gives the idea that it was memorized by Ananda only. So thus have I heard. Not thus have I witnessed. When discourses was made by Ananda about what others experienced it’s going naturally lack some information since Ananda did not personally experience it himself but heard it. While the person that experienced it with his students memorized it as he experienced it. If there is a conflict between two teachers and a discourses are made each will memorize it as told by each teacher. Each teacher went back in their home region to spread the Dhamma. And from there each lineages moved around India spreading Dhamma.
ALL this ofcourse is not real but just how complicated things might have been. 