Reality Subtext: Philip K. Dick actually did consult the I Ching while coming up with ideas for the book, much as Hawthorne does when writing his. This may imply he is something of an Author Avatar.
Science Marches On: The mentions of Nazi colonies on Mars and Venus by 1962. Both the ease of getting to those planets, and the habitability of the latter, were overestimated in The '60s.
What Could Have Been: Dick toyed around with several ideas for a sequel, but he couldn't bring himself to do more research on Nazi Germany, which he found profoundly depressing and soul-draining enough for one novel. Among them were:
The first draft of The Ganymede Takeover.
A story called "Ring of Fire" where the Nazis discover our world and steal nuclear weapons while a hybrid Japanese-American culture emerges.
An early version of Radio Free Albemuth where the VALIS satellite was communicating Hawthorne Abendsen's next book to him and keeping the Gestapo away.
Fake American: Several Brits play Americans, including Rupert Evans (Frank Frink), Rufus Sewell (Obergruppenfuhrer Smith), and Burn Gorman (The Marshal).
Fake Nationality: Americans Cary-Hiroyuki Tagawa (Trade Minister Tagomi), Joel de la Fuente (Inspector Kido), and Louis Ozawa Changchien (Kasoura) play Japanese characters. Danish actor Carsten Norgaard plays the German Rudolph Wegener.
Jossed: The cast and director mention in several interviews that the identity of The Man in the High Castle is not revealed yet. Which puts down the theory that Hitler is the man himself. Unless, of course, we're dealing with a Lying Creator.
Troubled Production: There were plans to bring the book into a TV series much earlier by different studios but fell through, the BBC in 2010 and SyFy in 2013, before Amazon studios finally took over.