I haven't understood the distinction you're trying to draw.
It means "A woman" but the use of "some" implies that the speaker doesn't know the woman personally. It also sounds a little casual, bordering on impolite (in respect of the woman). I wouldn't advise saying this to someone you are on formal terms with if there's a chance that she's his relative or friend.
Some woman is possible but extremely disrespectful, in most circumstances.
There was a cartoon in the Daily Mirror newspaper many years ago, about a character called Andy Capp, a working-class man who never does any work, always wears a cap, and is his own handicap.
In one instance, Andy is standing naked in a bathtub in his front room scrubbing himself when his wife Flo' comes in. Andy says to her 'Why don't you knock. You might have been some woman.' (I've disentangled the elisions indicating dialect speech.
The joke is that Flo' is, of course, a woman, but Andy meant any woman, a woman he wouldn't wish to see him naked, ie. any woman other than Flo'.
A certain woman means a particular woman, to whom the speaker or writer wishes to draw attention.
A woman means the same as some woman but is perfectly polite.
Because of possible overtones of disrespect and political correctness, and the sensitivity of people in general, these terms need using with care.