I personally don’t think they will have any problems reshuffling 1914 and the last days. It will wake some people up sure, but for the most part people will get excited over the changes and become more zealous as the “light gets brighter.” I can fix 1914, the last days, and the generation teaching for them all in one watchtower study. They can keep 1914 as still prophetic in the Bible so it ties into 1919. Here’s how....
The first Change will be in Matt 24:3 where Jesus is asked about the sign of his presence and the conclusion of this system of things. They can establish that the signs are two separate time frames. The Presence has its own signs, and the conclusion has its own signs.
Matthew 24:4-14 would apply to signs of Jesus presence with an emphasis on verse 8 where it says all these things are beginnings of pangs of distress.
The next paragraph in the watchtower study would say, previously Jehovah's witnesses believed that all of these signs were of the last days. Evidently, Jesus meant that these previous signs were beginnings of pangs of distress with signs for that specific event beginning in 1914. (Doing it this ways allows them to keep 1914 significant so that 1919 can be tied to it)
Matthew 24:15 and on would be the signs of the last days, beginning with the disgusting things standing in a holy place. They could even say that Matthew doesn't mention the word "days" until verse 19. Clearly indicating that this part of the chapter is meant to be a short period of time.
The next paragraph in the watchtower study would say that evidently the last days do not begin until the disgusting things stands in a holy place. A future event, which would coincide with the beginning of the great tribulation. This would indicate that the last days are a short period of time. By reading all of these signs we see that the only signs left are those that indicate the last days. Therefore, we know we are very close to the conclusion of this system of things.
Moving on to the generation teaching. Matthew 24:34 indicates that the generation that sees all of those signs would not pass away. Evidently this is a future generation that has to see all signs described in Matthew 24. Previously Jehovah's Witnessess while being sincere in their desire to understand scripture have incorrectly tried to interpret this prophecy. Through the light getting brighter we now have a better understanding of this prophecy as it is described in the scriptures.
And just like that, everyone would smile and nod and say it didn’t make sense the last days were so long. They would be so glad the governing body gave them a more accurate understanding.