I don't see that as a problem (see The Curious Case of Benjamin Button).If Before and After had been the blueprint for Kes instead of a one-off, it would have been more likely reworked a bit. For instance, Ocampa-human hybrids would likely have had a longer lifespan, so Linnis would likely have still been too young to marry anyone. Problem is, they'd already played the "kid grows up super fast" card with Naomi.