About dependences between tasks in the DAG of one job, and their start time.

"M5_3_4: means that task5 depends on both task3 and task4, that is, task5 cannot start before all instances of both task3 and task4 are completed.", which is read from "trace_2018.md(2.3 DAG of batch worloads)" to illuminate the DAG of a job, which emphasizes that task5 cannot start before task3 and task4 terminated.
However, in the real records in the batck_task.csv, there are many records not obey the rule of dependence above, for example, "R2_1,1,j_2,1,Terminated,87076,87086,50,0.2", "M1,1,j_2,1,Terminated,87076,87083,50,0.2", which are two tasks in the same job(j_2). We can see that task2(R2_1) depends on task1(M1), but the start time of task2(R2_1) is the same as task1's, both of them are 87076, which is confused me.
Can you please explain my confusion.

Start with section 2.3 of trace_2018.md and the referenced records in batck_task.csv, especially R2_1 and M1 for job j_2. Compare the documented dependency rule with the recorded start and termination times, then document an explanation of the apparent overlap.】【。

Written by the indexing model from the issue text.