I just wrote an email saying
I have written to you several times recently with various corrections but have yet to receive a response.
I'm wondering now whether this differs in normative content from "... but have not received a response yet". I feel that it does; it seems to carry more of an implication that it's not OK and I would have expected to receive a response by now – in fact I think that's precisely why I wrote it that way.
But in other contexts, there seems to be no such implication of expectations. For instance, in
The theory predicts additional particles, but evidence of their existence has yet to be found,
it doesn't seem to make much difference if we instead say "... but no evidence of their existence has been found yet". I don't feel that the first version expresses more of an expectation that evidence should have been found by now than the second version – if anything, it sounds a bit more like the evidence is bound to be found at some point than the second version does.
Can anyone throw some more light on this?