And why LumenGentleman should swing by more often. Scripture is his forte.
Bah ... the answers already given in this thread are more than adequate. :-)
My 2 cents: St. Matthew most certainly meant "knew" as in "intimate marital knowledge"; and his whole point in saying that St. Joseph did not "know" Our Lady "until" she had given birth to Our Lord was to emphasize that the conception/birth was indeed miraculous, not the result of any normal human marital relations.
He was definitely not
sharing this tid-bit of information in order to let his readers know that St. Joseph and Our Lady embarked upon normal marital relations after
the birth of Christ. As mentioned above in other posts, "until" can simply mean "up to this point" or "while", without implying that the situation changed afterwards. For example, the great Messianic Psalm (110, or 109 if you read the Douay) says of Our Lord, "Sit thou at my right hand, until
I make thine enemies thy footstool" - does this mean that when all things are
subjected to the rule of Our Lord, God the Father will ask Him to stop sitting at His right hand?
You get the idea.