NotFormer : Are they double dipping on the King of the North/King of the South prophecy, giving it multiple fulfilments?
Exactly. The King of the North and South were constantly changing identities in the stream of time (full details in chapter 10 of Your Will be Done on Earth, 1958, pp.220-263, and chapter 14 of Pay Attention to Daniel's Prophecy!, 1999, pp. 230-255).
Except, as we now know, between some time in the 2nd century and the second half of the 19th century when the kings vanished.
NotFormer : Would the new light have been the subject of watercooler conversations by JWs?
Yes, of those who keep pace with the chariot. There is a lot of historical trivia related to the world powers which is second nature to JWs.
NotFormer : Even that [Zenobia was King of the South] is confused: Syria is north of Israel/Judah/Judea.
Page 254 of Pay Attention to Daniel's Prophecy!, reports that :
An opportunity for Zenobia to expand her regal powers came in 269 C.E. when a pretender disputing Roman rulership appeared in Egypt. Zenobia’s army swiftly marched into Egypt, crushed the rebel, and took possession of the country. Proclaiming herself queen of Egypt, she minted coins in her own name. Her kingdom now stretched from the river Nile to the river Euphrates. It was at this point in her life that Zenobia came to occupy the position of “the king of the south.”—Daniel 11:25, 26.
So at the time Zenobia became King of the South she was queen of Egypt (south of Israel/Judah/Judea), and that is where the warfare with the King of the North (Aurelian) initially took place.