I get skin checks yearly and fortunately have been all clear.
Now, here's a case of melanoma that was not found through a skin check: my boss developed an enlarged lymph node shortly after starting work in my office. No other symptoms, just a very large lymph node on his neck. He got it checked out, tests were run and turns out he had melanoma, even though after a very thorough skin check was done after finding the lymph node, not a single mole was found.
He was staged at 3B and underwent treatment, which was successful.