Just a few thoughts after reading you most recent post, zorka. I don't know if there is any coherence to them, but these are the things that seemed to trigger off in my mind:
What you've touched on here, zorka, is very interesting. It reminds me of some research I did for a paper in an archaeology course, in the course of which I was exposed to a theoretical school of thought within history that I did not realize existed. This school of thought questions whether the past ever really happened at all, or at least if we can know if it ever really happened. Sort of an agnosticism of history, maybe.
I didn't get too deeply into it, becuase it touched on the subject of my paper only tangentially. Consequently, I don't really know much about it, although I'd love to get into it more deeply. The gist of it, as it concerned processual archaeology (with its interest in the general process of how sites come to exist) and its lack of interest in any kind of specific history, seemed to be that there was no point in speculating on the particular historical events involved in creating any particular archaeological site because there was no way of knowing what those historical events were, and because we can't know those specific historical events, we can't even be sure the past ever happened at all. We weren't there; we didn't witness it; therefore, how can we even know it happened. The fact that particular artifacts exist is not nearly enough evidence that it did because we cannot determine with any certainty how they got there.
I'm not sure I've got this all exactly right - as I said, I didn't get into it too deeply. But it seems to have some relation to the historicity and it's implications as you discussed them. How can we know, really, which lighter was in FDR's pocket, if we were not there? Even if there is a letter of authenticity, we weren't there so we cannot know with certainty. And if we cannot know for certain that the lighter was in FDR's pocket, how can we know that FDR even existed? Well, you might say, we've got pictures of him, we've got historical references to him. Yes, this is true. However, even though there are, for example, historical, extra-Biblical references to Jesus, there are those who argue that there really was no historical personage who correlates to the individual called Jesus who is spoken about in the New Testament. And so it goes...how can we ever really know, absent personally witnessing a person, a place, an event? Personally, I find the idea that history never happened to be a bit silly, sort of on a par with "is the universe all in a dream I'm having?" But it seems, from what little I read, to be something that has been argued in seriousness.
Also, as I read your post I kept thinking of Heisenberg's uncertainty principle, although it does not seem to be directly relevant. And, too, I thought of the idea of a holographic universe that does not become concrete unless someone is looking. So, too, history in Dick's novel seemed to depend on who was looking at it and from what vantage point.
And, too, Dick seems to be posing the age-old question of, "What is Truth?" Or, is there one objective Truth? The Germans and Japanese really won the war. That seems to be the Truth, or at least the reality, that the characters are living in. No, says the I Ching, the Allies won the war. So, which is it? Both cannot be true. Or can they? I don't think Dick answers that question but, looked at one way, his novel seems to be asking it.
Well, my mind hurts now, from all this philosophical speculation. As I said, these were not meant to be coherent arguments, just things that the book and the previous posts made me think of, for whatever that's worth. Maybe two cents?