The WTS uses the 'second prophetic fulfillment' concept to build new doctrines. That way, even if you read the original text and see the obvious conclusion (for example, that the 'other sheep' referred to non-Israelites), they can add an additional interpretation that applies to the present day (that the 'other sheep' refer to a non-heavenly hope). If we point out that this is not the original meaning, they will say that they are not challenging that interpretation; they have received divine guidance towards a second, modern fulfillment.
They did this with the "generation" teaching. It's nonsense on stilts, once you step back and see it without the cult blinders. But it is effective on those who are still in, because it doesn't mess with the original (and often clear) explanation. It adds a completely new one.