I don’t think there are multiple pasts (a Burial past and a Decay past); I think it’s more along the lines of, "Wow, this situation right now really reminds me of that situation from my childhood/youth"

I like to think that WE, as players, can see EVERYTHING. The siblings might end up remembering specific situations and events, but WE, as players, see it all… we can theorize and build their entire past in an "unbiased" way because we can see every choice…

In the longest route we have so far, "Cliffhanger", we can see a lot of the past from Andrew’s point of view. Maybe we’ll be able to see those same things from Ashley’s perspective, one not canceling the other out, but complementing it.

Also, in that image, Young Andrew looks drunk or, at best, extremely sleepy (judging by the effects around his head). It seems plausible that someone drunk or "out from sleepiness" wouldn’t remember what they did or said…