The lists are riddled with errors...

The lists miss even those people who do file the IRS forms
We personally know 6 people who renounced citizenship at different times in the last few years, filed all forms with the IRS, and received their confirmation certificate. So the IRS has two sources of information about them. Nonetheless, their names do not appear in the lists. Unfortunately, none wish to have their information made public, so we cannot disclose their names as proof.

http://renunciationguide.com/Data-On-Renunciants.html