I am struggling sort of, with this, because of the verse that goes "He did not know her until she brought forth their firstborn son." I've seen the explanation for this but I'm struggling with trying to understand why it doesn't mean what it plainly says. However, I'm not trying to cause problems, and I realize that the notion of her PV does not really affect me in my everyday life
The problem is that it doesn't plainly say that Mary and Joseph had sex after Jesus was born.
The definition of the word "until" is simply to make a statement about a condition up to the point of time referenced. It does not give us any information about what happened after that point of time or imply that the condition automatically changed afterward. But people assume the condition changed if that's what they think should happen.
When the Bible says Joseph did not know Mary until Jesus was born, because most married people have sex, people assume that means they did. But it's simply an assumption.
For example, if I'm going to dinner and leave my kids with a babysitter and tell them to "be good until I get home" does that mean I'm telling them that they only have to be good until I get home but after that they don't have to be? Of course not. Nobody assumes that to be the case because they know that's not what I'm implying. I am simply stressing the importance of their being good for this specified timeframe. Which is exactly what Matthew is saying in his Gospel -- he is stressing the importance of knowing that Joseph and Mary did not biologically create Jesus in the normal fashion. He is not telling us anything about what happened afterward nor does he intend to.
If you look throughout Scripture that are a multitude of examples where we know that the word "until" does not mean the condition changes after the point of time of the until. Some examples:
Genesis 8:5 “And the waters continued to abate until (eōs) the tenth month.” When one reads this text about the great flood, one might assume after the tenth month the waters ceased to recede and the flood was over. But you would be wrong. It is simply a marker in the story – a checkpoint where the tops of the mountains are now seen. The waters continued to abate after the checkpoint. The condition does not change from before the usage of "until" to afterward.
2 Samuel 6:23 – “And Michal the daughter of Saul had no child to (eōs) the day of her death.” Is the implication here mean she had children after she died? Of course not. The condition does not change from before the usage of "until" to afterward.
1 Timothy 4:13 –
“Till I come, attend to the public reading of scripture, to preaching, to teaching.” Is the implication here that once Paul comes Timothy would no longer preach and teach?
Matthew 28:20 –
“and lo, I am with you always, to (eōs) the close of the age.” Is the implication here that once the age ends Jesus is no longer with us?
Bottom line is we make an assumption as to whether or not there is a change of condition after "until" based upon what seems most likely to us. But it's only an assumption and nothing else.