NT use of the plural "scriptures"

[Solo]

So, to make my interests clear: I am coming fast to believe that the plural of "scriptures" was first used by Mark to be understood recursively as including Paul's and his own writing. Matt and Luke thought it was clever (or something like that) and continued the tradition. Frank didn't, but that was because he was Frank.

Then, of course, verses which have "scriptures" in them in Paul's corpus would be fake because the interpolators did not realize they were using an expression common in the flock of their own time but an anachronism to Paul. See what I mean ?

If one runs with the mainstream pack, the NT authors were guided as instruments of the holy spirit. See for example THE PROBLEM OF ANONYMITY AND PSEUDONYMITY IN CHRISTIAN LITERATURE OF THE FIRST TWO CENTURIES by K. ALAND. We know they regarded the LXX as Holy Scripture (singular) and we also know that they were being commissioned by the Holy Spirit to author additional scripture in the form of the Greek NT. Consequently the finished product NT + LXX might naturally be referred to in the plural.

I am thinking just that: the plural indicates the inclusion of internal Christian documents that were commonly revered and later became canon.

Best,
Jiri