I've never known her to be wrong

I'd never known teachers to be more strict about any other school rule.

The teachers in that school "were" very strict about that rule.

I had never known teachers to be more strict about any other school rule.
من هرگز قبل از آن معلم ها را نسبت به هیچ قانون دیگری سختگیرتر ندیده بودم

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این توضیح و مثال از دیکشنری وبستر خیلی خوب مطلب رو روشن می کنه
✦Someone who has been known to be or known to do something has been or done that thing in the past.

• We've known him to work all night to meet a deadline. = He's been known to work all night to meet a deadline.

• I've never known her to be wrong. [=I do not know of any time when she has been wrong]
من هرگز ندیده ام که او اشتباه کند
یعنی من هرگز زمانی از گذشته را به خاطر ندارم که اشتباه کرده باشد
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I've worked with him for many years, and I know him to be an honest man.
من او را به عنوان فردی صادق و درستکار می شناسم

• He's been known to do this kind of thing before.

The authorities know him to be (= know that he is) a cocaine dealer.
مسولین او را به عنوان یک دلال کوکائین می شناسند