I may be castigated for saying this but with memory all things are possible, BUT that possiblity doesnt mean they arent true. I find it interesting that you T told you to make up scenarios that 'could' fill in the blank spot. That would have me nervous in itself. While my memory wasnt very conscious.. there was always a knowing about the who and the what that was burried yet not completely unknown. Everyone doesnt have to be like that though. I think when you try to force a memory to emerge it becomes frustrating. One thing that helped me was letting my memory be and moving to something else and working on other more present issues. Often doing that will trigger other memories of the past and helps you really become more comfortable with your memory itself.

Whatever you do try not to feel upset whether you remember or dont. I have this meditation and it says... 'Nothing you can learn or know can make you a better person than you are right now. You are able to take on whatever healing you need at the moment with what you have inside. '

I have found that true in my healing process. I'm not sure if it is universal, but it spoke to me.. best of luck.
Hope that helps.