Regulations change frequently — often more frequently than statutes. And it is, of course, critically important to base your advice to a client on the latest version of a regulation.
This page lists several good options for checking to see if you have the current rules on your topic.
The most official source for updates to the California Code of Regulations (CCR) — and particularly for proposed regulations — is the California Regulatory Notice Register (also known as the "Z Register").
The "Z Register" is published weekly, and is available in PDF format from the Office of Administrative Law, and in print.
Both Lexis and Westlaw do their best to incorporate (or at least link to) changes in their versions of the California Code of Regulations within a couple of weeks of the change.
Many California executive branch agency web sites have good, current information about new and/or proposed regulations. If you know the agencies that have oversight of your clients' issues, check their sites frequently to stay on top of the latest developments.