The Independent Police Complaints Commission (IPCC) is conducting investigations involving three police forces into whether the ex-Lostprophets frontman could have been brought to justice sooner and whether his celebrity status had any impact on police inquiries.
The commission said it has served gross misconduct notices on three South Yorkshire Police officers, two Bedfordshire Police officers and a South Wales police officer as part of its ongoing inquiries.
Singer Watkins is currently serving a 35-year prison term for a string of child sex offences.
Three independent IPCC investigations are ongoing into the on the response of South Wales Police, Bedfordshire Police and South Yorkshire Police to allegations that Watkins was abusing children.
IPCC commissioner Jan Williams said: "We are making good progress with our three independent investigations and as result of our inquiries IPCC investigators have served notices on six further officers as part of the ongoing investigation."