GSTN Chief Navin Kumar, in an exclusive interview to CNBC TV-18 Managing Editor Shereen Bhan, says that only 16,000 GST Returns in Form GSTR-3B have been uploaded so far; Urges industry not to wait till August 20 deadline, while clarifying that there is no plan for extension yet; Also says that system can withstand the deluge towards fag end, but taxpayers may experience some delay