Если у нас 2 действия [в прошлом], мы используем Past Simple для более позднего действия и Past Perfect для более раннего действия.
Она сказала, что они меня увидели.
А если у нас 3 действия? Ведь нет такого времени, как Past Past Perfect.
Она сказала, что они обнаружили, что он... (видеть меня раньше).
Это тоже будет Past Perfect?
She said they had found he had seen me.
Вопрос заключается в том, что в этом случае можно понять это так, что "увидели" случилось одновременно с "обнаружили", но ведь это действие было раньше. Если бы было время Past Past Perfect, было бы легче: She said they had found out he had had seen me.

She said they found out he had seen me. ¿

Тогда получится, что "said" и "found out" были одновременно, как

Она сказала, что они выясняют, что он видел меня

Выяснили - past. А то, что выяснили раньше, чем сказала, по-моему, подразумевается. Как в русском. Я сказала, что я была в кино. То, что я была в кино раньше, понятно по умолчанию.

Ну, неужели

Она сказала, что они выясняют, что он видел меня

Будет переведено как

She said they find out he had seen me

Тогда не будет согласования

С «выясняют» Ваше предложение разве имеет смысл?

Она сказала, что они выясняют, видел ли он меня. Я думаю, для «выясняют» здесь будет past progressive - they were... ing.. Типа they were looking into...

First of all, SAID is a bad example here because in reported speech, the tense are unreliable and lose their original meaning. A more significant example would be "She FOUND OUT [past] that they HAD CONFESSED [pluperfect/past perfect] that they HAD STOLEN [plusquamperfect] the money." This is how linguists normally distinguish these forms, although in the general literature, all three names are used as a blanket term for the past perfect. Outwardly, there's no difference between the pluperfect and the plusquamperfect - they both take HAD.

How very interesting! I thought "plusquamperfect/plusquamperfekt" is something that exists only in German.))

Then how to distinguish, whether these both Past Perfects happened/were happening at the same time or one of them was before than the other?

Как можно украсть и сознаться в краже одновременно? Are you not overthinking that?))

Я не про этот конкретно пример, а про любой другой, в котором тоже будет два Past Perfect, но и примеры будут таковы, в которых оба варинта логичны.

Я не про этот конкретно пример, а про любой другой, в котором тоже будет два Past Perfect, но и примеры будут таковы, в которых оба варинта логичны.

Michael, I can’t even imagine such a context. Can you give me an example?

Hm, what about this:

We discovered that when he had arrived she had been sleeping.

If we dont have "we discovered" we have two options:

1) At the same time
When he arrived she was sleeping

2) Before
When he arrived she had been sleeping

But here we have it and "arrival" was before "discovering what makes it to be in Past Perfect + sleeping - whether it was simutaneously with "arrival" or before.

HAD BEEN SLEEPING would be before the arrival

Like

We discovered that she had been sleeping before he had arrived

?

Yes. There’s a point in the past where he arrived, and before that point, the woman was asleep.

So, the only prompt to understand these actions didn't happen at the same time is "before"? Without this word both actions are Past Perfect what makes all of this ambiguous

If these actions happened simultaneously, one would be in the past perfect and one would be in the past continuous: When the man arrived, she was sleeping.

Also, in your sentence, there’s no need for the past perfect: “They discovered that when he ARRIVED, she WAS/HAD BEEN sleeping.” The overuse of the past perfect is as annoying as its misuse.

https://www.grammarphobia.com/blog/2012/02/past-perfect.html

But how can we use "when he arrived" if it was earlier than "They dicovered". Using Past Simple for both makes me think they happened at the same time but not one earlier than the other,

P.S. Thank you for the link.

I had bought [past perfect] the car with the understanding that there was a warranty.”

Am I right that when we go to using Past Pefect, there happens some kind of tense shift and actions happenng at the same time when the Past Pefect happened are described with Past Simple/Past Continuous? If the next action was before we use Past Perfect.

...that there was a warranty.
Means the warranty at the time of buying the car.

...that there had been a warranty
Mean the warranty was before buying the car

It' like when using Perfect it looks like Perfect but acts like Past SImple - simultaneous action go with Past Simple/Contiuous, earlier actions go with Past Perfect.

No, what the article is pointing out is that they shouldn’t have used the past perfect at all. They should have said “I BOUGHT the car with the understanding that there was a warranty.”

But in that sentence there's an action before which the buying of the car happened:

“Last July, the brakes on my car failed [simple past]. I had bought [past perfect] the car with the understanding that there was a warranty.”

So, firstly he bought the car thinking it had a warranty, then the brakes on his car failed. I guess this sentence is correct because we have an action before which the Perfect action took place.

This one

“I had sold him the car in January with a standard three-month warranty. He had refused to pay an extra $100 for a one-year warranty.”

is not right because there aren't any time points/verbs before which "had sold" and "had refused" happened.

It's like Past Perfect/Continuous - is "-2" level
while
Past Simple/Continuous is "-1" level.

We can't use "-2" without having "-1".

And as I understand

“Last July, the brakes on my car failed = -"1" [simple past].

I had bought the car = "-2" [past perfect]

There was a warranty. = "-1" [simple past]

However the third one is equaled with "had bought" but not with "failed" though it has "Past Simple".