You said:It is hard not to conceive of them as NT books when they are on the page which lists the NT books and leaves it up to the reader to include or exclude them from the canon.
A) He counted them as NT books
B) He allowed people to exclude them from the Canon
It can't be both ways: he can't say they were part of the New Testament and also not 100% essential (and if he did think they were 100% essential, he wouldn't let people choose).
Scripture is, in essence, necessary and non-negligible. Anything that is not totally necessary cannot be Holy Scripture.
On a related note, if we can step back for a moment and realize that Luther was willing to let people disregard 15% of the New Testament, that should shock us and lead us to question him a bit more I think.
within the context of the SA Article IV point of agreement it makes no difference whether Mary was virgin or ever virgin
I disagree. The Smalcald Articles were (as their subheading read) "Articles of Christian Doctrine" and Part 1 was a Creed. If Martin Luther wrote that Mary was "pure, holy, ever-virgin" in this Creed, then that can't be disregarded. The words of a Creed are very important and weighed carefully.