Marilyn Vos Savant's 228 score was taken when she was 10. The IQ is scored differently in adults and kids; when you're a child there is a ratio taken between your mental age and actual age, whereas in adults you are measured against the general populations IQ distribution.
She has since taken IQ tests which put hers at the much more reasonable (though still very high) 186. The highest must belong to one of those in the Giga society whose founder is Paul Cooijmans.
As for these other 'individuals' claiming to know those with IQ's over 200, these are falsehoods. It has been extrapolated backwards that Sidis would have had over 200, but this is difficult to base one's beliefs on.