1914 used to be a load bearing wall. It couldn't have been taken away without everything else falling down. It is still their most significant date in the sense of JW history so they can't admit to being wrong about it - not for a long time yet. But I don't think its holding the building up in the same way anymore. If 1914 was taken away, people would be unhappy but I think the structure of belief would still mostly keep standing.
The reason they don't mention 1914 is because it is connected to the new overlapping generation doctrine which is just so ridiculous, embarrassing and confusing that nobody wants to talk about it. So it exists but is ignored. More and more it'll become a doctrinal vestigial organ, like an human appendix, that people know they have in their body academically, but never need to think about. It need not be taken out as long as it does no harm.