The 1914 teaching, by itself, isn't a huge problem for them (at least, as long as we ignore that Russell's interpretation was that 1914 was the date of the end itself, not the beginning of the end). The problem is that they added the "this generation" teaching to it, which created a sense of urgency, which is useful for end-days cults.
They quietly dropped that part in 1995, and that should have solved the problem. But without it, they don't have the sense of urgency anymore. So they came up with "overlapping generations." It's a really bad idea that they are stuck with for at least a while longer, and which I expect they will finally drop for good once the old guard are gone.