grammar - Past Perfect with only one verb (action) in sentence

I was taught that:

The past perfect is used to emphasize that an action was
completed before another took place

e.g.:

I was very tired as I hadn't slept well for several days

But there are many examples of sentences where this tense is used with only one verb, e.g.:

She had pricked her finger on a rose thorn

His breathing had become uneven.

Over the years her beauty had faded a little

She had not shed a single tear during the funeral

It had rained for four consecutive days

Someone had slashed the tires

Vandals had smashed all the windows

There is no indication that action was completed before onother action took place, so in all these sentences I would use the present perfect or the simple past.

As you can see all these examples come from Longman English Dictionary, so I presume they are grammatically correct.

So what is the reason of using the past perfect in these sentences?