Well, I can truly understand your frustrations. How infuriating it must be to have been kept in the dark for so many years.
Having said that, after my first Dday at the end of July, when affair had only lasted about a month and was supposedly over . . . he couldn't even remember some of the details that had "just" happened during that one month period, let alone five years before.
When Dday 2 hit on Christmas night, five months later, we went through similar "not remembering" things. To this day I remember more than he does about certain things. Things he knew initially, but has since forgot, particularly when it comes to dates.
I truly believe my husband wasn't trying to get out of telling me things he said he didn't remember. He actually got out his calendar to jog his memory when I asked about dates.
He really doesn't "want" to remember and doesn't obsess over every detail like I do.
Once I mentioned why a certain place was a trigger for me and he didn't get why. I told him its because we had both seen "her" there and it was just a few days after they had "declared their affection for each other". Nothing had technically started yet, he had previously told me that that's basically when it started. And yet, now when he thinks back to our running into her three days later he completely didn't think it was after they had told each other they were attracted to each other.
And this boggles my mind, as your husband's "memory lapse" boggles yours, because it was all around his dad's funeral, which makes it quite easy for "me" to remember. He was facebook messaging "her" the night he was staying up late for his brother to arrive from out of state because of the funeral. That's was the night they disclosed their affections. Then a few days later, the day AFTER the funeral, we ran into her like an hour away from home. I think his brain is split. While they had declared their attraction for each other, nothing official had happened yet, so when he thinks of the day we saw her, he doesn't have any guilt, which is why I think he doesn't correlate why I trigger. (Yet even if nothing at all was going on yet, I STILL would trigger from having seen her there, a place we seldom go.) Anyway, apparently he knew she was there either from facebook posts/messages or from texting. I'm not sure but I do have to say it was REALLY weird when he made a point to take a detour to drive by the cafe she was hanging out at with her sister, so we could say hi for ten seconds in the parking lot. The way he was acting, all secretively, but yet in a fun way, I thought surely we were going to see someone we all might think was fun to "happen upon". But this was just weird.
But I digress. While it was a few days after they had verbally affirmed attraction, per his initial divulge of information, months later he looked back at that day and completely didn't think it was "after".
My point is, I really do think it's reasonable that your husband might not be remembering the things he says he doesn't remember. Guys brains really are different with these sort of things than women's. It's just the way it is. That's not to say he might actually remember and doesn't want to tell you for some reason. But based on my experience with my husband, and knowing how my his brain works with remembering or not remembering things unrelated to the affair, I'm inclined to believe him.
Maybe think about other instances where your husband either remembers or doesn't remember things you think he should that he'd have no reason to hide from you. Maybe figure out a way to ask him about some of those things without him knowing your playing detective. Just a thought.
Hugs to you. I hope you can get whatever information you need to help begin to heal. It's so sad that it's taking this long to get info, because every time there's new revelation, new info, your healing starts over. To some degree anyway. I can't even imagine having to go through this years later, having already been aching with pain all that time.
Take care of yourself.