PAST PERFECT

The Past Perfect expresses the idea that something occurred before another action in the past. It can also show that something happened before a specific time in the past.

Ex:
he had visited the city several times.
we had not booked in advance.
Had you ever visited U.S.A.?

Formula:
Verbal
S + had + past participle (V3).
S + had + not + past participle.
had + S + past participle.

Nominal
S + had + been + adv, adj, or noun.
S + had + been + not + adv, adj, or noun.
Had + S + been + adv, adj, or noun.

we use the Past Perfect to show that something started in the past and continued up until another action in the past.

Unlike with the Present Perfect, it is possible to use specific time words or phrases with the Past Perfect. Although this is possible, it is usually not necessary.

If the Past Perfect action did occur at a specific time, the Simple Past can be used instead of the Past Perfect when "before" or "after" is used in the sentence. The words "before" and "after" actually tell you what happens first, so the Past Perfect is optional. For this reason, both sentences below are correct.

Examples:

She had visited her Japanese relatives once in 2003 before she moved in with them in 2006.
She visited her Japanese relatives once in 2003 before she moved in with them in 2006.