We meet Dobby in Chamber of Secrets. And no other house-elf. And when we finally meet up with others, we go blink, blink, blink, because it turns out, Dobby is an atypical house-elf. Delighted to be free.
When we meet up with something we assume it's typical. (Not just for world-building. Put a character out on stage, and we assume it's a typical behavior for him. Introducing a character in an odd moment can take a lot of work to overcome.)
People sometimes have this trouble with hobbits. The glimpses of hobbits in their normal behavior at the beginning and end of Lord of the Rings doesn't prevent people from thinking of hobbits as beings that go on adventures, when they are in fact stolid, unimaginative, smug, insular, and complacent, and the typical hobbit thinks leaving the Shire, or Breeland, is stupid. Tolkien's own description of the typical hobbit is to take Sam, and now imagine him without his poetry and his fascination with elves.
This is one reason when it's so hard to write a SF or fantasy mystery. How are we to know that's a discrepancy and so a clue if it could be just incluing us to the world?