Is the reference time point for past perfect derived from the context or from within the sentence?

Question

The past perfect is a verb tense used to show that an action took place before another time point in the past.

Should the "another time point in the past" be the time point of the context or the time point within the sentence?

Or it depends?

Example 1

Although I had bought a present for my girlfriend and put it on her desk, her father hid it away.

Is the reference time point the action of "hiding it away", which is within the sentence?

Example 2

Although the theories had been taught worldwide and had become common knowledge, they still amazed me last week when I heard them.

Maybe there is a context, and the reference point is the time of background of the context, not the time point of action of "amazing me"?

Answer 1

To use your terminology, the reference time is the time point of the sentence.

In both cases there is a (short) narrative: "Her father hid the present", The theories amazed me". And there is a time being described in that narrative. It is implicit in the first example "the time of hiding", but explicitly "last week" in the second.

The past perfect is used, in both cases, to refer to actions that occurred prior to the time of the narrative, but having an effect at the time of the narrative. In these simple examples the time of the narrative is given in the sentence so it is trivial to rephrase them to avoid the past perfect:

I bought my girlfriend a present and left it on her desk, but her father hid it away.

(coordinating conjunction "but" so the narrative can just proceed chronologically)

The theories are taught worldwide and are considered to be common knowledge, yet they still amazed me when I heard about them last week.

(You don't need any past form here!)

However, see Past Perfect with a time reference in a separate sentence The time point may be given by another sentence as in that example (slightly edited for the lols):

Cactus Buddy and Pond Power have announced the creation of a joint venture titled Waterthorns. The two firms had stated their intent to form the joint venture back in 2012.