Ok, researching this a little further with jwfacts.com and the original "Birth of a Nation" article, I think I have found a discrepancy (albeit one that is created by Watchtower writers). jwfacts notes:
The 1260 days of Revelation 11:3 are not to be confused with the 1260 days of Revelation12:6. This second period is described as "extending in the Northern Hemisphere from the spring of 1919 to the autumn of 1922. This was a period of refreshing recuperation and reorganization for the restored John class." Revelation - It's Great Climax is at Hand! p.184
So there are actually two 1260 day periods (according to WT): the one in Rev 11 mentioned in the Nov 2014 article; and one in Rev 12 mentioned in the Birth of a Nation article in 1925.
If I've missed something, let me know.
Confusing as hell.