Why would later humans create a creature that there would be historical records of because it would happen after Crono and crew defeats him? I would think that if humans would have the capability to create Lavos in the future that they would know better because they would have some type of record of what it is capable of. It's an interesting theory, just not a plausible one. Even if the Guardia record didn't survive, keep in mind that there were other people from other time periods that knew what happened. I doubt any records from Ayla's or Magus' would survive that long, but there is still Robo. Even if he did turn into the Prometheus circuit, he probably had a way to record what happened. Somebody in the future is bound to find one of the records because there would be 4 at least floating around.