At this point, each of you (in your thoughts) is wanting the instructor to provide a black & white explanation of when a formal 8-D is required. Unfortunately, the answer is that the only time an 8-D is �required� is when a customer requires it.
Each company provides an internal threshold. It is typically somewhat subjective. There is no �absolute� in so far as when or how far. Many companies use a Review Board. But - each has it�s own path.