Watson,
Verses and accounts can be invented. For example, Mark 16:9-20; 1 John 5:7. All prophets were advocates of Law of Sow and Reap. (Isaiah 3:10, 11; Mark 4:24; Galatians 5:7 …etc.) Such teachings make existence of religions unnecessary but religions want a God who forgives. Hence they wanted characters who are known for their spirituality but occasionally fall into sin—hence David’s sins were to be invented—just like account in John 8:2-11 was invented. (My Favorite Passage that’s Not in the Bible)
Even very big subject too can be invented https://www.jehovahs-witness.com/topic/5654969410650112/there-no-heavenly-calling-wishful-thinking-jws
New Covenant of NT has nothing to do with its supposed basis in Jeremiah 31:31-34, hence a new teaching.