Keep in mind that a present perfect casts its predication in the present tense. It does not narrate past events, it mentions past events which give rise to a present state.
That is why formal English does not permit a present perfect to be used with a temporal adjunct which does not include the present moment, the Speech Time at which the sentence is uttered. (You will occasionally find this rule violated in improvised, conversational discourse; but even there it is comparatively rare.) Thus, this is acceptable:
okI have often visited London.
But this is not:
∗ I have often visited London in the 1990s.
Today, in the 20th century is a timeframe which excludes the present. Consequently:
Sentence 1) is acceptable if it appears in a text written in the present century, but would be of questionable acceptability if written fifteen years ago.
Sentence 2) is acceptable if it appeared in a text written during the 20th century, but it would not be acceptable if written today.
There is a great deal more about this at What is the perfect, and how should I use it?, especially §§ 3.1 Grammatical meaning, 3.2 Pragmatic meaning and 4. When and how should I use the perfect?.
∗ marks a usage as unacceptable
First sentence
I used to live in the US for a year before I became a teacher.
The expression used to describes a situation that no longer exists, or ceased to exist at some specified time. In this case, it means that the speaker
moved to the US, lived there for a year, moved away from the US and then (probably straight afterwards) became a teacher.
Second sentence
I had been living in the US for a year before I became a teacher.
This sentence does not feel quite natural because both the past perfect had been and the conjunction before indicate that something occurred before something else: in addition, for a year specifies a time interval. That sounds like it ought to define quite a complex sequence of events.
It could be made more natural by eliminating one of the before-indicators, like this:
I was living in the US for a year before I became a teacher.
This sentence describes a situation where the speaker moved to the US, lived there for a year and (probably directly after that year) became a teacher.
I had been living in the US for a year when I became a teacher.
This sentence describes a situation where the speaker moved to the US, lived there for a year and directly after that year became a teacher.
Alternatively, you could eliminate the time interval specifier, like this:
I had been living in the US before I became a teacher.
This sentence describes a situation where the speaker moved to the US and stayed there for a while, but left some time before becoming a teacher.
Best Answer
Because the main verb of the sentence--disclosed--is in the past tense and the (completed) actions described by the verbs engage and scrap occurred before that disclosure. As has been mentioned, the sentence is not written in the clearest manner possible. That said, its verb tenses are correct and bog standard.
To address the other options:
just adds another layer of opacity to the writing and either means (a) exactly the same thing as the terser phrasing or (b) means that some other entity was responsible for engaging these companies in suspicious transactions. Sense (b) doesn't seem supported by the rest of the context, so it's just making poor phrasing worse.
similarly can mean (a) exactly the same thing as the past perfect or (b) shift it into the passive. Again, sense (b) doesn't seem supported. The difference between the first sense and the past perfect is that the same action is being described, but without reference to the occurrence of the main verb. It suggests a more distant relationship between the two verbs.
places the question solidly before the completed action of her move to Topeka.
places the question in the past and removes any connection between the time of the two verbs, leaving it unclear whether she did in fact ever actually leave.