A: I watched that movie last night.
B: Hm, I watched it 2 days ago.
There is no need to use the Past Perfect here. In general, experience shows that the Past Perfect should be used with caution. The fact that something technically happened before something else does not automatically trigger the use of the Past Perfect.
First I graduated from the University of Oxford and then I started a new job, but then I had to leave it.
Here we simply enumerate certain events. Correct me if I am wrong, but my opinion is based on my study of the Queen's English and later American English which tends to dispense with the Past Perfect in most cases.
Student or Learner