Does a hat and cane come with that dance? Really can a woman have a baby after she dies. No. So why the DRA uses unto instead of 'until' in 2 Sam 6:23. Because it is evident the author is communicating she would not bear children period and death is the end of mortal life. So I hear unless someone changed the definition of death too. So Joseph we are told did not know Mary 'until' the birth of Jesus Christ. If you want to redefine until as it is clearly stated in that passage to fit a traditional doctrine, fine but don't cast stones at other Christians who see "until" meaning what it is.
And that's the point of the example: the use of "until" does not mean she did afterward; any more than its use in your example means Joseph had sexual relations with Mary afterward.
I've given examples in scripture and in use today where it did not carry the meaning you give it.