I think most of us, in the past Sab, have done as you have above and restricted the "Scriptures" referred to by the writer of Timothy to the accepted O.T Canon.
But in line with B.O.R's comment above, could not the writer be saying that any "scripture" (sacred writing) could be considered "God-breathed" if it was able to "teach, to correct, to show people how to live"( to paraphrase) , that way the canon would in fact never need to be closed.
Remember the probable late date of Timothy 1&2 , the writer would have been well aware of the writings circulating, Gnostic and other "Gospels" etc, and by this argument of his, he would be seeking to qualify all the writings of Paul and his own to Timothy , as scripture, and maybe distance them from some of the more obviously errant ones.
It is possible to read his words that way, no ?