You don’t need to prove attaining a magga phala to anyone else, LDF.
– You can verify for yourself, and no one else can confirm or deny that.
Furthermore, different people get rid of sakkaya ditthi in different ways.
– There is a sutta where the Buddha gave an analogy. One time, a bhikkhu went around asking other bhikkhus (who had declared attaining the Sotapanna stage) how to describe the Sotapanna stage. Each one gave different descriptions of the Sotapanna stage.
– That bhikkhu got confused and complained to the Buddha. The Buddha gave an analogy of asking someone to describe a tree that had a unique trunk (black), unique flowers (bright red looking like pieces of red meat), and unique leaves (specific unique shape). Some people would identify the tree as having that unique trunk, some others describe it with flowers or leaves. But they all had seen the tree!
– I don’t remember the name of that sutta.
– P.S. There are two main conclusions reached when one gets to the Sotapanna stage: One would have “seen with wisdom (panna)” that (i) there is no “permanent self” traveling the rebirth process (it happens via Paticca Samuppada), (ii) it is fruitless AND dangerous to be in the rebirth process (because most rebirths are in the apayas).
By the way, here is a post that describes “temporary bhavanga”: “Bhava and Bhavaṅga – Simply Explained!“