Oh, I don’t disagree, kaylasdad, though it may well have cemented Snape’s position against V. The prophecy occurred before Harry was born, and V didn’t kill him until he was nearly a year old. OTOH, I am convinced that Snape and Lily did have some kind of respect for each other, mainly because I am convinced that Snape is “that horrible boy” whom Petunia heard talking about dementors.
Also noted second time through: one of the first potions Harry makes for Slughorn is Draft of the Living Death–just a little reminder from JKR.
And note that the recipe is no longer merely powdered rood of asphodel mixed with an infusion of wormwood (cf – Harry’s first Potions class), but now involves valerian roots, extract of sopophorous bean, and some complicated bits of stirring.
Sure, Snape may have tinkered with the recipe to inprove it, but it doesn’t seem very realistic to suppose that such a drastically different preparation shoud have the same name. It would tend to render most accepted antidote efforts pointless.
Maybe the asphodel/wormwood combination is just a basic recipe, one that produces the desired result, but can have unfortunate side effects. The other ingredients (which must be added in a prescribed manner) serve to buffer those effects. The valerian root, for example, might prevent the drinker from appearing to be undergoing rigor mortis. The sopophorous extract might eliminate vivid dreams/nightmares sometimes caused by the wormwood. None of this would change the basic character of the potion, and the active ingredients remain asphodel and wormwood. Think of it like certain aspirin products containing caffeine; the caffeine isn’t a painkiller–the aspirin still fulfills that role–but the caffeine makes it more effective in certain cases.
Yeah, I like to retcon things. That just means the Potterverse provides me with some extra entertainment.