Yes, there may be interpretation, but the authority was scripture. Scripture is over which they might argue.
Yes, they may cite someone's tradition, but the authority was scripture. Not the tradition per se.
Here's Christ in Luke 24:27.
And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning himself.
Here's Peter in 2 Peter 1:21.
For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.
Here's Paul in Acts 26:22.
Having therefore obtained help of God, I continue unto this day, witnessing both to small and great, saying none other things than those which the prophets and Moses did say should come:
Everyone good? Any disagreement?
So, SS is in OT.