Correct tense for events which happend long time ago but still have direct connection with present time

Solution 1:

It wouldn't be Harry had disappeared because that would require two times and two actions to be involved - "When I went to the house, Harry had disappeared".

You could use Harry disappeared if you are stating it as a fact. "Harry? Oh yes- Harry disappeared"

You could use "Harry has disappeared" if his disappearance has present consequences - "We can probably sell his car now, because Harry has disappeared"

There is nothing inherent in present perfect that limits how far back in time it can go, but in practical terms the further back it goes, the less likely it is to have present consequences.

Solution 2:

You know, Harry has disappeared.

This sentence sounds like Harry just disappeared recently.

You know, Harry had disappeared.

Using had makes it sound like Harry disappeared, but subsequently reappeared. I think the most correct version of the three is:

You know, Harry disappeared.

While it is ambiguous, it doesn't lead the listener to think the disappearance was recent or resolved, like the other two versions. Better still would be:

You know, Harry disappeared 20 years ago and has never been found.

Solution 3:

The past tense in English (and, as far as I know, every other language) says that something happened in the past, period. We do not have different tenses for the recent past versus long past. If you say “Harry disappeared”, that sentence of itself, with no further information, does not say whether he disappeared twenty years ago or twenty seconds ago. You would have to supply additional words to specify.

If you say, “Harry had disappeared”, that is placing Harry’s disappearance relative to some other event in the past. The context should specify that event. Like, “When the bills became due, Harry had disappeared.”