Your references to other scripture for how it uses "till" or "until" is hardly addressing the scripture that says Joseph knew not his wife "till" she gave birth to Jesus.
Matthew 1:24 Then Joseph being raised from sleep did as the angel of the Lord had bidden him, and took unto him his wife: 25
And knew her not till she had brought forth her firstborn son: and he called his name Jesus.
There is no point for Joseph to marry Mary if she was to remain a virgin when marriage means God is joining the two to become one flesh to build a family. And they did have a family after Jesus because He had brothers and sisters too.
Matthew 13:54 And when he was come into his own country, he taught them in their synagogue, insomuch that they were astonished, and said, Whence hath this man this wisdom, and these mighty works? 55
Is not this the carpenter's son? is not his mother called Mary? and his brethren, James, and Joses, and Simon, and Judas? 56 And his sisters, are they not all with us? Whence then hath this man all these things? 57 And they were offended in him. But Jesus said unto them, A prophet is not without honour, save in his own country, and in his own house. 58 And he did not many mighty works there because of their unbelief.