Read what is says, not what you think it says. It says, St. Joseph knew her not before she gave birth. In other words, the child was not Joseph's. That is all it says.
If Holy Tradition now comes around and supersedes historical facts
Now. It consists of historical facts. There is no "if".
Read what is says, not what you think it says.
You are projecting.
You also deleted the "firstborn" from the passage, and your Greek rendering of the improper genitive preposition 'έως' is wrong - it should be rendered "until". But I already went over this with you weeks ago and you didn't refute it then. Heck, your interpretation is even in conflict with the Douray-Rheims translation and the RSV (along with scores of Protestant English translations).