She must have seen him a week ago.
She may have seen him a week ago.
She cannot have seen him a week ago.
Having seen him a week ago, she is always thinking of him.
She speaks of having seen him a week ago.
She seems to have seen him a week ago.
即使不用助动词，也不用在分词、动名词或不定式的形式里，偶尔也有用完成时态而用ago的 。例如：I have long ago given up that habit.这里语气重在“早已” 。
附：
时间段+ ago用于“过去进行时”例：
《新时代英汉大词典》第52页ago词条
You were doing it a moment ago, before you spoke to me.
刚才你还在做那件事儿呢，就在你跟我说话前那会儿 。
《牛津英语用法指南》（第三版）第47页ago词条
Where’s Mike? ~ He was workingoutsideten minutes ago.
迈克在哪儿？~ 十分钟以前，他还在外面干活儿呢 。
2008年高考英语，辽宁卷阅读理解B 第三自然段第一句话：
A few weeks ago, Wesley Autrey was waiting at a Harlem subway station with his two little girls when he saw a man fall into the path of a train.

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【完成进行时 完成时态】2017年3月25日

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