[tapu]

I don't think relativizing to "my truth" makes a real difference in the examples. It's exactly what goes on anyway. People often dispute what is "really" the truth. The child claims, "Nossir, you never told me that!" The mother responds "Yes, I did." Or even, "You know I did." In this case, the power balance is unequal and generally the mother "wins." When power is more balanced, people argue and bring evidence to support "their truth."

I do think words have power and that a change like this is often part of a process that changes understanding as well as usage, but I don't think the case is quite as strong here as you make it.