Note also that, in canon, the Priori Incantatem effect (and therefore plausibly also the Priori Incantato spell) will show the specific person who was AKed. If V.’s wand shows him killing baby Harry, and baby Harry is right there and conspicuously alive, that would be fairly specific evidence in favor of the “survived the Killing Curse” hypothesis.
Note also that, in canon, the Priori Incantatem effect (and therefore plausibly also the Priori Incantato spell) will show the specific person who was AKed. If V.’s wand shows him killing baby Harry, and baby Harry is right there and conspicuously alive, that would be fairly specific evidence in favor of the “survived the Killing Curse” hypothesis.