Cal. COM § 8206

(a) If a security certificate contains the signatures necessary to its issue or transfer but is incomplete in any other respect, the following apply: (1) Any person may complete it by filling in the blanks as authorized. (2) Even if the blanks are incorrectly filled in, the security certificate as completed is enforceable by a purchaser who took it for value and without notice of the incorrectness. (b) A complete security certificate that has been improperly altered, even if fraudulently, remains enforceable, but only according to its original terms.