These are not extra-biblical citations, but would seem to support for
your previous conclusions.
Though the plural, GRAFAS, is used, it seems as though Peter is referring
to some of Paul's writings, at least, as being Scripture in II Peter
3:15-16.
Also, in I Timothy 5:18, GRAFH is apparently used to refer to both Deut.
25:4 and Luke 10:7.
Fred Nofer