I have found that it is easier to just admit I don't remember rather than try to act like I do. The latter is just so stressful and, sometimes, humiliating. Even though we have now shared many, many dissociated memories with each other we still frequently have people tell us about things we should remember but don't. Like, all. the. time. I just tell them outright - sorry, I have a terrible memory, and I often ask them to tell me more about it. More often than not I don't have any recollection of any of those events at all. So bizarre, but just a part of a life not lived by me.
ETA: I have done a lot of memory integration work, so I now know a lot of that stuff. The things I tend to not know about are the fun things - social interactions, relationships, funny memories, stuff like that. Kinda sad really.