That's irrelevant to the use of the word "until."
Until means until; it does not necessarily mean the converse afterward even in English today - as I illustrated previously.
Eos ou in Matthew is used to tell that Joseph had no part in the conception of Jesus, that he had no sexual relations with Mary prior to the birth of Christ. This is obviously a very important fact to tell.
Other examples:
"And Milchal, the daughter of Saul, had no child until [eos] her death." and "'Sit at my right hand until [eos] I make Thine enemies Thy footstool." (Mark 12:36)
I neither of the uses of eos, is it meant that the converse occurred or will occur after the event.
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.