Never. 1914 is the only JW dogma; it can never be changed because it explains the validity of the entire church structure. Blood and disfellowshipping may pass away, but 1914 always gets doubled-down.
The GB may have their problems. But they do -- it seems to me -- genuinely believe what they teach. You simply need to understand what they teach as core doctrine, which is simply that they are the group that Jesus selected to be the one, holy, catholic, and apostolic church in 1919 (or 1918, I can never get that straight). It can't change because without it, they can't justify their existence; say what you like, they have to justify their status.
The single unalterable JW belief is that their inherent superiority led to Jesus selecting them above every other religion. They don't believe any of their other teachings -- at least not in the sense that they wold hold them if they didn't want to. So, they can change the meaning of a word -- generation -- they can change blood if they wanted, anything, really. But the claim that they cracked the secret code and that something really important happened in 1914 can't change.
It is the founding event of the JW self-conception. It is their Resurrection.