Hi Yogician
I don't see MM online at the moment, so I'll try to give you an answer.
Yes, the expression "as yet" means up to the present time (or up to a specified time). To me it often sounds more formal, and I'd say it places a little added stress on the idea of 'now'.
The phrase 'as yet' can begin a negative sentence, but the word 'yet' (with a similar meaning) cannot. You'll often find 'as yet' in a sentence with a negative meaning or sense, but without the word 'not'. So, 'as yet' is also similar in meaning to the word 'still'.
I think you'll be able to understand my explanation better with some examples.
In a negative sentence (with the word 'not'):- We do not know his exact whereabouts as yet.
- As yet, we do not know his exact whereabouts.
In a sentence without the word 'not' (but with a negative meaning or sense):- His exact whereabouts are as yet unknown.
- His exact whereabouts are unknown as yet.
- As yet, his exact whereabouts are unknown.
- Are his exact whereabouts as yet unknown?
- His as yet unknown whereabouts are the main topic of conversation.Maybe MM (or someone else) will be able to give you some additional input.