关于过去完成时什么时候用,像只要一个句子还有before和过去式那一定有过去完成时了?

过去完成时：
1.概念：以过去某个时间为标准,在此以前发生的动作或行为,或在过去某动作之前完成的行为,即“过去的过去”.
2.时间状语：before,by the end of last year(term,month…),etc.
3.基本结构：had + done.
4.否定形式：had + not + done.
5.一般疑问句：had放于句首.
6.例句：As soon as we got to the station,the train had left.
By the end of last month.We had reviewed four books