若语境需要，不定式的完成式完全可以连用 ago。如：

Talks were to have begun two weeks ago. 会谈在两周前就该开始了。

I seem to have read the book two years ago. 我似乎两年前就读过这本书。

The bridge is believed to have been built twenty years ago. 那座桥被认为是在20年前建成的。

另外，情态动词后面接完成式时也可以连用 ago。如：

He ought to have reached the house some time ago. 他到达那所房子应该有一段时间了。

He ought to have reached the house some time ago. 他应该早就到房子那儿了。

The council ought to have condemned these houses long ago. 地方议会早就应该宣布这些房子不适宜住人了。

This bill ought to have been paid weeks ago. 这份账单几个星期前就应该付清了。

The stars must have formed 10 to 15 billion years ago. 这些恒星一定形成于100亿至150亿年前。

He must have started writing his book a long time ago. 他一定很久以前就开始写这本书了。