We (you, I, and the Church) are in agreement that the Didache is NOT Scripture and is NOT authoritatively applicable to the whole Church. The fact that it is one source of some of the evidence contributing to "Sacred Tradition" does not mean that everything in it is sacred. You seem to have a fundamental misunderstanding here.
" Now hold on....you can't appeal to "sacred tradition" when it fits the catholic need. It either applies to the whole church or not... some could say I agree with "X" or I disagree with "Y". It's not an either or"
Here's how we use these sources: we look for converging lines of evidence.
There's a difference between "proof-texting" and "finding converging lines of evidence." The evidence (not "proof") found in early Apostolic-age sources gets real traction when it shows up again and again, indicating that the practice or belief was Church-wide. For instance, if there's something in the North African sources, the Syrian sources, the Anatolian sources and the Greek sources that's in agreement, that's evidence that doctrine X or practice Y was not just a local custom or opinion, but was part of a wider Church consensus. This takes scholarship.
In the words of the Vincentian Canon, we are loyal to "That Faith which has been believed everywhere, always, by all." [The Commonitory, ch. 2, by Vincent of Lérins.] Rather than go into a multi-paragraph explanation, I'll just direct you to an excellent source (and not even a Catholic one!) This is from the Orthodox blog, Orthodoxbridge.com, and explains (to a Reformed dialogue partner) the way we can be "sourced" by Tradition without considering any one non-Scriptural source as being equal to Scripture.
I may not get back to this until tomorrow, but meanwhile do go to the link. It's pretty clear, seems to me.
Unless they are all parroting what the others are parroting without independent research...