undiagnosed but suspected with early symptoms

Good Morning - how do you know the symptoms are related to cognition as opposed to continued ADD? I feel like I am always questioning my own judgment about whether or not my DH is getting worse or I am over reacting. He is only 54 but had a TBI when he was 43. He never regained his full executive functioning. I feel like I go round and round with conversations because he never fully answers or comprehends what I am saying or asking. He has always misplaced items, been unorganized, and scatterbrained. I am having difficulty knowing if this behavior has always been there and I am just noticing it more or whether it has gotten much worse (which I believe it has). His father had very early onset aphasia and died at 62. Any thoughts or experiences?