1. Why send ballots until verified.
2. There's no document verification. Anybody can enter someone's name and social security number and get a ballot delivered anywhere.
3. I still don't trust the ballot gets thrown out if there's a mismatch.
In order to be 100% safe, there should be only in person voting with a voter id. Anything else is open to abuse.
The process is described on the same website you linked to: https://www.sos.ca.gov/elections/voter-registration/same-day...