Here's a thought. Think about what good fiction does. It tells essential truths even if the details are imaginary. A story isn't just something to get lost in; that's not why the best fiction captures us. It captures us because an imaginary story a writer dreamed up 100 years ago resonates with us today; it says something vital about our OWN experiences, our own wounds and hearts.
I believe this can be true for our own stories as well. Even when we're not clear about certain details, the emotional truths stay with us. You may not remember the chronology of X traumatic event (and in fact, it's unusual for that to happen--traumatic memory isn't encoded that way neurologically). But the impressions--of feeling terrified, trapped, hopeless, whatever it is--I think there's a terrible and important truth in those things. And that is the stuff of therapy.
I think that as long as we keep that awareness that the details may remain fuzzy forever, but the emotional themes are real material, then we can trust the therapeutic process and eventually get better.
Just my $.02.
LG