In general, I would say that if the child qualified for extended norms, there's no reason not to use them. If I (as a report writer) were worried about a skeptical audience, then I'd report both scores -- with and without extended scoring -- and explain the difference.
Note that having a 19 does not mean that the extended norms needed to be used -- it's only if they got a raw score *higher* than what was needed to make the 19 scaled score. But the tester should be on the lookout for that when scoring the test.
