Invalid registrations may easily go undetected. It does specify procedures for doing so. And if such a name is voted in that period, it is re-activated. Even though NVRA requires such removals to occur at least 90 days before a federal election, most state registrations do not close until 30 days before elections, creating a 60-day window within which new registrations can be lodged, and leaving little time for due diligence. Many states do not have centralized voter registration.
Registration is maintained on a local basis.
Even those states that do maintain some form of statewide voter roll may not perform routine matching procedures among the component jurisdictions. Certainly, there is no mechanism to match records of one state against another. Many voters assume that when they move, their old registration is canceled. This may not be the case even within a state, and certainly not across state borders. Thus, we believe there is an undocumented prevalence of voters who are registered in multiple jurisdictions and multiple states.