It makes no difference whether the prediction is made before or after the fact exists: rather, that it makes a prediction that a fact confirms once it is known. The most popular (and scary!) example of this is the current problem of antibiotic-resistant bacteria. I don't need to spell out the details, since there's so much available on Google about this.
But consider the predictions that Natural Selection makes concerning isolated species - geographically isolate, as on an island; or genetically isolated, as with 2 genetically similar populations that, for whatever reason, tend not to interbreed. The predictions of natural selection (and sexual selection) are verified wherever we look! From Pygmy Elephants on Malta to Giant Predators in the ancient America - the theory makes predictions that are confirmed by the literal mountain of evidence that continue to come in with further examination of the fossil record.
But consider the predictions that Natural Selection makes concerning isolated species - geographically isolate, as on an island; or genetically isolated, as with 2 genetically similar populations that, for whatever reason, tend not to interbreed. The predictions of natural selection (and sexual selection) are verified wherever we look! From Pygmy Elephants on Malta to Giant Predators in the ancient America - the theory makes predictions that are confirmed by the literal mountain of evidence that continue to come in with further examination of the fossil record.