Sorry, maybe I am dense but you lost me on that one.
If saying "X was A until B" does not mean X was not A after B...
Likewise, your assertion that you will be non-Catholic until you die does not mean you will be Catholic after then.
Again, saying something did not occur "until" does not necessarily mean it happened after. I'm referring of course to the phrase "knew her not UNTIL.."
This also helps explain why this scripture was not any problem to the Church's belief in Mary's perpetual virginity before the reformation and the same is true for the leaders of the Reformation - all of whom were well-versed in scripture. This scriptural find and problem arose only relatively recently.