I agree with you Witzend. At first, because my mum was young/65 when it started, I felt it was her right know what was going on and I thought it might help her to tell people what she had since she was hiding away from social situations and feeling stupid and judged all the time. But, it became clear that she was much happier not addressing it and now, like you, I believe she cannot keep a meaningful memory of her illness and for this I am very grateful.
Yes, personally I think it can be a blessing if the person is not aware, though I do realise this can cause its own problems. But who on earth wants to be conscious all the time that they have a horrible disease that has no cure?