"How can an eternal Truth be true for one generation and not be true for the next?"  

The creation story in Genesis was supposed to be an eternal truth.  We now know it's not literal eternal truth.  It's myth and/or allegory.  You treat it as if it's literal history, maybe to prove your points, but I find it just an example of an impediment to truly discussing how the Spirit operates in the Body of Christ.  God is not denying Himself when supposed eternal truths are enhanced, modified, understood differently, given a nuance not previously thought of, brought into closer conformity with His truth, expanded to include more of His children and on and on and on.  Teachings have always changed in the Church, always.  To pretend they haven't is self willed delusion.