Changes in affixes , power shrine , ascension enshrined with power shrine combined , hirling debuffs , debuffs, your element , your weapon , etc. Also item quality, empower talent/talents in general and more.
Many many factors into account. I think he experienced the placebo effect with the Ascensions buffing DMG of stat point. The only real buffed DMG would be Enshrined - Power Shrine if lucky.
When doing the calculations , I realise just how easily to accurately predict DMG and me seeing that damage I predicted and if never changed even at eternal ascension.