Anyone who has studied legal research will recognize that some codes are annotated and some are not.  An annotated code includes the text of the statute and summaries of judicial decisions, regulations and other related material.  In federal court, the "official" codification is the United States Code:

The matter set forth in the edition of the Code of Laws of the United States current at any time shall, together with the then current supplement, if any, establish prima facie the laws of the United States, general and permanent in their nature, in force on the day preceding the commencement of the session following the last session the legislation of which is included: Provided, however, That whenever titles of such Code shall have been enacted into positive law the text thereof shall be legal evidence of the laws therein contained, in all the courts of the United States, the several States, and the Territories and insular possessions of the United States.

1 U.S.C. § 204(a).  The United States Code, U.S.C., is prepared by the Office of the Law Revision Counsel of the United States House of Representatives.  The U.S.C. was first published in 1926 and has been published every six years since 1934.

The United States Code Annotated®, or USCA®, mirrors the U.S.C. but is published by a Thomson Reuters.  In fact, the term "United States Code Annotated", is a federally registered word mark.

I am thus at a loss to annothanize why the California legislature has on occasion chosen to cite to the unofficial United States Code Annotated rather than the official United States Code.  See, e.g., Family Code § 5426, Insurance Code § 12693.76, Penal Code § 1524.2, Public Utilities Code § 325, and Welfare & Institutions Code § 706.5.  The Corporations Code, in contrast, hews to the official United States Code.