But If I want to point ascerted fact "of finding" unspecefied time in the past without emphasising to an evidence right now, nothing more

Like " I have lived in London" ascerted fact unspecefied time in the past so with highly ASSUMTION I don't live right now (in a context it isn't interesting where I am but fact of expirience in the past)

I found the key refers to an unspecified time in the past, although in context it might be understood to mean "The key I've been looking for -- I have it now."

"I found the key" - OK, it might be understood like "informer" accentuate on obvious time in the past of course in context (there's specifier ... 1970, some time ago or some action affected, was background ... ...). More interesting exactly when or how happned, rather than a result

Please see the addendum to the answer.

Something's wrong here. Isn't before a time marker? We can't use the Present Perfect with time markers.

@SovereignSun: You're wrong about that. The restriction on time-markers when used with the present perfect is that they cannot exclude the present. "Before (now)" doesn't exclude the present; it derives its meaning from the notion of the present. There's nothing awkward or unidiomatic about "I have done it several times in my life".

Compare: I know that guy from somewhere. I've seen him before. google.com/…

@Tᴚoɯɐuo Illogical, since before now isn't the in present anymore - it is in the past. Either I'm too tired or English is changing by the minute.

@SovereignSun: You're approaching this in the wrong way. It has to do with the speaker's origo. "Before" means "before now" -- it involves the present, it is not disconnected from the present. Perhaps there are things you still have to learn about English?

There's nothing awkward or unidiomatic about "I have done it several times in my life". – Tᴚoɯɐuo -> "I have found it (again -> THE key) " several times in my life.

Does it always "mandatory meaning" I have found the key I possess the key now? Must I use Present Perfect ONLY, if thise condition (meaning) is right?

@Farkhad Ismatov: Language does not occur without a context. But let's imagine a minimalist context: if I walk into the living room and say to a person in my family, I have found the key!, they are likely to conclude that I have been searching for a key and that I found it moments earlier. That is what they are likely to infer from the absence of additional temporal qualifiers. In practical contexts, listeners typically eliminate remote possibilities and opt for the salient, most probable meaning.

ell.stackexchange.com/questions/13255/…, "What governs the use of the perfect is not the content, the meaning it expresses, but the purpose it serves. If you want to know whether to use a perfect, look at what you are trying to accomplish. What really distinguishes the perfect from the deictic constructions is focus: are you talking about state of affairs current at Reference Time or are you talking about the prior eventuality which in some sense gave rise to the current state of affairs?"

@Farkhad Ismatov: what are you trying to say?

Speaker can easily focus on the prior eventuality or result as you said: "That is what they are likely to infer from the absence of additional temporal qualifiers. In practical contexts, listeners typically eliminate remote possibilities and opt for the salient, most probable meaning".

Two things matter: 1) Am I saying something happened in the past as of the present moment, and the specific time is not important, just the fact it is the past and 2) Is the situation true at the time of speaking. 2) always applies, but condition 1) needn't apply. "I have found the key [as we speak] but my sister took it away from me" versus " I found the key and my sister took it away from me". See the difference in focus?

Imaginary real-life example: A: Hi! B: Hi! A: Have you found the key?/Did you find the key? B: Yes, I've./Yes, I did.

"I found the key and my sister took it away from me" it seems like element of narration

It is referring to two events, both in the past. The simple past is silent with respect to any present relevance.

Is this the most real algorithm of thinking to use PrPerf in aforecited situation?