The term 'vipassana' is rarely found in the discourses. What exactly, in terms of detailed explanation, do the suttas impart about vipassana? Not very much, in reality, if not close to nothing.
It follows teachers over the years have done their best to explain vipassana. The dhammas listed above, such as bhaṅga-ñāṇa, bhayatupaṭṭhāna-ñāṇa, ādīnava-ñāṇa, nibbidā-ñāṇa, etc, are certainly not alien to the sutta discourses . The terms ādīnava (danger) and nibbidā (revulsion) are used abundantly in the sutta discourses. Bhayatupaṭṭhāna is found at least at the very end of MN 130, which states: "Clinging they look upon with fear".
Anāpānasati may indicate one contemplative effort but the discourse offers little explanation. Is the term vipassana found in the Anāpānasati sutta? Or consider, the terms sabbakāyapaṭisaṃvedī
as found in Anāpānasati. Do they relate to vipassana? What do they mean, exactly?
The opinions on these subjects are numerous because the suttas often do not provide detailed explanations.