Changing usage of past-perfect constructions in American and British usage

I notice a great many American speakers using the construction had loved as a preterite, that is, a simple past tense. I also hear the simple past tense used in instances in which I was taught to use the past perfect tense.

Is this a widespread trend, to use the past perfect construction as a past tense construction, and to use the past tense instead of the past perfect tense to indicate action that precedes the past action that has just been mentioned?

Examples are

Before I met her I heard about her

instead of

Before I met her I had heard about her

and

I had heard about her yesterday for the first time."

Neither Microsoft Word nor WordPerfect likes it when I use the string had had. For example,

By the time he got to Phoenix, he had had enough to drink to make him stagger."

Is the past perfect disappearing from American usage? Is it also disappearing from British usage? And is the past perfect construction being widely used as a simple past?

This is my opinion as an American. The past perfect is not gone, but it is my impression that we don't use the past perfect when the simple past is sufficient to relay the intended meaning. Most of the time, as in your sentences, there are other constructions to supplement the simple past and convey it as perfect past.

I heard about her before I met her.

The temporal marker "before" supplements "met", turning this simple past into the past perfect. But the following certainly wouldn't sound foreign to an American.

I had heard about her before I met her.

or, using the contraction...

I'd heard about her before I met her.

As for the following...

Yesterday, I heard about her for the first time.

This isn't past perfect. It's simple past, but an American might say the following.

I had heard about her when I met her yesterday.

Without the temporal marker "before", the past perfect is essential to convey the meaning. However, for that sentence to sound natural, I'd have to hear it as a response to a question, such as, "Didn't someone tell you about her?"

As for the following statement:

By the time he got to Phoenix, he had had enough to drink to make him stagger.

This is something that Word will fuss about and I'll ignore or modify to mollify. Word isn't the expert; it's a tool to help those who aren't. If you're an expert and Word is catching stuff, either it's wrong or you're too tired. An easy way to modify the above sentence and more closely resemble how I would actually speak it is to use a contraction.

By the time he got to Phoenix, he'd had enough to drink to make him stagger.

On the other hand, you can turn the verb around.

By the time he got to Phoenix, he had drunk enough to make him stagger.

The past perfect isn't gone in American English; we don't always use it when we don't have to.

As an American speaker of English, what is happening (as experienced by me listening to media and native speakers in everyday life) is that the past perfect is NOT used when it should be.

The first two sentences in the OP's questions (in fact all three) are typical utterances in English. There is nothing ungrammatical about them in fact.

Americans do not use the "had loved" in lieu of preterite (simple past).

Here is what somewhat uneducated speakers do:

They use the SP incorrectly in conditionals.

If I did it, it would have been because I wanted to. to mean: if I had done it

If he went, he would have seen the movie. to mean: if he had gone.

In other words, they don't put the PP after IF for past-tense conditional utterances. This is extremely common.

And sometimes, they leave out the PP when it would be better to their intended meaning. Now, this is very difficult to google or use NGRAM for. You just have to trust my ear because I can't search database recordings for the types of utterances I am discussing here.

Very often, when the past perfect could be used by a speaker to be more precise, they don't use it:

So, both:

They had arrived before us.

AND

They arrived before us.

are grammatical. But in listening to people, they might mean, but don't say, the first. Sometimes, it doesn't matter in terms of their conversation. At other times it does.

That said, I find that the more educated the speaker, the less they use only simple past instead of past perfect when past perfect would be more appropriate to their meaning.

Also, when two speakers get into a muddle or do not understand each other, you often also hear one speaker say to other: you mean had arrived before you?

This is almost unconscious because these kinds of speakers aren't really aware of grammar, but they know instinctively in these situations that had + past participle means that the action preceded some other in the past.