Hello, Anushka:
My Chambers Thesaurus may help you, by showing you some �synonyms�, (words which have a similar meaning.)
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YET (adverb)
1) UP TILL NOW ... until now, up to ths time, up till then, by now, by then, now, already, as yet, so far, still.
OLD-FASHIONED STYLE = hitherto, heretofore.
FORMAL STYLE = thus far,
2) IN ADDITION ... still, even, too, also, further, furthermore, besides, moreover.
COLLOQUIAL = into the bargain.
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YET (conjunction)
1) BUT ... however, nevertheless, nonetheless, anyway, even so, all the same, just the same, for all that.
FORMAL STYLE = notwithstanding.
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First, you must decide what Part Of Speech the word �YET� is. Then choose the correct Category.
So, your first sentence could be re-written: (conjunction)
"BUT, it has been found in some companies that by far the healthiest people are ..."
And your second sentence: (adverb)
"What is surprising is that, UP TO THIS TIME, we are STILL to develop successful ways of dealing with ..."
I hope that this helps you.
Les Douglas