I'm using an exercise from the Purdue Owl to understand tense usage. The exercise, which uses an excerpt from Alex Haley's Roots, can be found here: https://owl.english.purdue.edu/exercises/2/22/51
Here's the sentence I'm having trouble with: "Since my forefather had said his name was Kin-tay (properly spelled Kinte), and since the Kinte clan was known in Gambia, the group of Gambians would see what they could do to help me."
In this case, Haley uses both the past perfect (had said) to indicate something that started sometime in the past and continued up to another time in the past and the simple past (was) to describe something that was true for some time in the past. It seems to me that in this case, the past perfect and simple past tense are interchangeable. Haley could just as easily written "since my forefather said his name was Kin-tay" or "the Kinte clan had been known," although the latter example wouldn't have been as graceful. Are these two tenses sometimes interchangeable? Or is it a matter of duration? Have I missed something?