I don't think you're strange for not remembering. Some people just have a mind for those sorts of details.

I do remember quite a lot, except for DS1 's first 9-ish months or so, because I had horrific PND, and my brain just didn't work well at all, I do remember DD's and his major milestones at that time, though. I have written a lot of it down, but I just remember it anyway also, it's rare I need to check if I am right or not.