Roughly 463,000 voters in California do not provide a drivers license or last four digits of their social security when they register to vote, according to a statement given to me this week by California's Secretary of State.
"Approximately ninety-eight percent of all registered voters in California include a driver’s license or the last four numbers of their Social Security number when registering to vote." -SOS
A state report from May says there are 23.1 million registered voters. 2% of that is roughly 463,000.