Past perfect usage exceptions

[MarceloT821]

I would like to understand more deeply some exceptions on the usage rules of past perfect tense.
The SC strategy guide states that "When the meaning of a sentence is already clear, the correct answer may not use past perfect to indicate an earlier action".
The example used to exemplify this exception is: "Laura locked the deadbolt before she left to work".
The guide mentions explicitly the words "before" and "after" as words that make the sequence of events clear enough not to use past perfect, but it stops far from requiring that those are the only words that can do that.

I was paying attention to that exception when i was trying to solve the problem set questions of the Verbs chapter.
In that set, the example number 4 uses the word "already":

• She already woke up when the phone rang

I immediately thought this example is correct, but the strategy guide requires this sentences to be converted to past perfect:

• She had already woke up when the phone rang

If I would change the sentence to use only the word "before", then, I guess, the past simple would be acceptable:

• She woke up before the phone rang

I would really like to understand if the decision to use past perfect is a matter of meaning or of the words selected to mark the time reference. If the words are what matters, then I would like to know whether "before" and "after" are the only such words?

Just to be explicit on what is driving me to try so much to understand this issue, I want to add here my original doubt, which is driving me crazy.
I have seen an official GMAT answer which mentions two events at different past times, both are expressed using past simple. Since i cannot copy here the original phrase i will just create a phrase with a very similar structure:

• It was not until 1995 that the school had a principal who did not come from the city

I accept this sentence has correct tenses but understanding the reason is something that i still cannot grasp.
The biggest obstacle might be the double negative. If the same sentence would say the opposite ("It was not until 1995 that the school had a principal who came from the city") I would analyze it in this way:
There are two events:

1. The school had the principal


2. The principal came from the city

Its obvious that he came from the city before he became the principal so I would naturally correct the phrase to use the past perfect: "It was not until 1995 that the school had a principal who had come from the city".
But it seems that I am wrong and the past simple is enough here. So my questions would be:

1. Is the double negative somehow related here to the proper selection of verb tenses?


2. Is the phrase "It was not until 1995" somehow responsible for not needing the perfect tense? Would the sentence "The school had a principal who did not come from the city" be correct?

Thank you for helping me understand this tricky topic.

[tim]

I would really like to understand if the decision to use past perfect is a matter of meaning or of the words selected to mark the time reference. If the words are what matters, then I would like to know whether "before" and "after" are the only such words?

In general, you should NEVER assume there is a comprehensive list of anything for SC. That's simply not how the English language works. Please also understand that it is a false dichotomy to ask whether something "is a matter of meaning or of the words selected". Everything is a matter of meaning OF the words selected.

Its obvious that he came from the city before he became the principal so I would naturally correct the phrase to use the past perfect: "It was not until 1995 that the school had a principal who had come from the city".

Hold on ... If it's so obvious that coming from the city preceded him becoming the principal, then that is precisely WHY we don't need separate tenses! Using the past perfect is needed when it would otherwise be impossible to tell which event came first.