The reason Voldemort had been defeated originally was because Severus Snape had begged him to spare Lily's life and Voldemort agreed. That's the reason Lily's sacrifice can protect Harry, because she had a choice.
As he had left Britain and not become a Death Eater this did not happen. Instead, when Voldemort had attacked the Potters he killed them all and moved on to killing other enemies. Lily and James were Voldemort's enemy, even if not have the prophecy, Vol still tried to kill them.