Voldemort used horcruxes, obviously (that's what the five hidden items in the elemental pattern are)

I would hesitate to call this "obviously". Certainly, there's the Pioneer plaque, but as for the elemental pattern, all we actually have is Quirrell remarking on the fact that Harry's ideas have an elemental pattern, and Harry himself failing to realise it. There's nary a hint that Harry's guesses correspond to anything that actually happened.