The picture on the outside panels is based on an illustration in the Nuremberg Chronicle (1493), with several changes.
Subtractions include:
1) the bambini at the top building a tabernacle from cut branches
2) the crystal orb representing the earth
3) the two columns at the sides, which since about 1516 had been a personal emblem of Charles V
4) the blank shields that could be filled in by the owner of a copy of the book.
Additions include:
1) a pope's crown
2) a book
3) a circular island, resembling the map in Thomas More's Utopia.
These are updates: around 1528, against the advice of Thomas More, the island king Henry VIII, who had written a book that was well received by the pope, was on the way to divorcing the queen and breaking with the Catholic Church.
The circa 1528 date comes from the allegorized Nahuatl picture writing on the inside panels, but perhaps the English connection is enough to suggest an approximate date on its own, at least to a time window when the king's decision was still up in the air.
added note: An object on the throne in the Nuremberg Chronicle illustration might be a book, but it is more prominent and recognizable on the triptych.