If the tests were reported to that level – and we're talking 2002 here – the fact that the child appeared to be from another relative wouldn't necessarily put the caseworkers at ease. (Was the child handed off between siblings as a form of welfare fraud?)

They got lucky with the thyroid test in the Boston (Keegan) case. The chimeric cells can be anywhere, in any proportions. (There's no guarantee the complete thyroid, or complete ovary is a single genome... so the 'luck of the stick' could change the results.)