I've often heard as a rejection of evolution: Well there should be thousands of transitional fossils. My response: How would you know if they were?

So we can see some very dramatic examples of "transitional" forms in animals like Archaeopteryx or Tiktaalik. Animals which are displaying signature examples of anatomy which are characteristic of two or more different groups.
But leaving aside the normal observation that fossilization is incredibly rare and discovery/description rarer still, my question for creationists who think there ought to be transitional forms littering the landscape is this: How do you know you aren't looking at thousands of transitional forms?
Without seeing the animals directly on either side of this one...how would you determine whether or not it's transitional?
Evolution predicts that genotypic change will be gradual, much less phenotypic change...so how does the creationist reasonably conclude that specimen I is not transitional between specimen H and J?