I know, that's the idea, but if you create a task list john will see all his tasks and he will be able to choose in which task to work. If you want to know from the history logs which process create each task you have the Task.TaskData.workItemId reference that helps you to find the process where that task instance was created. Notice that there is a named query defined for that reason:
<named-query name="TaskByWorkItemId">
<query>
select
t
from
Task t
where
t.taskData.workItemId = :workItemId
</query>
<!-- hint name="org.hibernate.timeout" value="200"/ -->
</named-query>
Cheers