yet with present perfect

Question

"we did not know about national skinheads; they did not exist yet"

"we did not know about national skinheads; they have not existed yet"

I know what means the first: it means that we did not know about skinheads because they did not exist but skinheads were going to exist after this time (when we did not know) and that they still exit.

Does the second sentence mean the same, the "yet" means that it will happen,does it mean that skinheads were going to exist very very shortly after this time (when we did not know)and that they still exist.

Is this sentence possible?

I know I already asked for it but not with present perfect

Answer 1

I haven't completed this yet.

I haven't gone there yet.

We haven't looked for it yet.

The above sentences mean that the subject intends to perform the action, but right now, did not perform it (yet).

They have not existed yet

This seems grammatically correct, but sounds a bit weird because "exist" isn't typically something wills oneself to do, but something that "happens" to someone - and is typically not something that someone makes a choice about.

I will exist tomorrow

Unless you planning not to exist for some reason, or something very strange/intense is going on and obvious from the context, my thinking is "well ... of course, why wouldn't you exist?"

Thus,

They did not exist yet.

this sounds the best.

Answer 2

For your sentence to be correct, you need to have the past perfect in the second clause. This is because the first half of the sentence sets the reference time to some point in the past. To reference a time in the past, you use the past perfect. You have to say:

We did not know about national skinheads; they had not existed yet.

In addition, "yet" refers to the past, not to the future, even the very very near future.

I have not coughed yet.

This sentence says nothing about the future. Both the present perfect and the "yet" talk about time up until the present moment.