Legal Question in Civil Litigation in California

Yes, but the opposing side would likely not be able to have it tossed out for that failure.

A motion to amend a pleading before trial must:

(1) Include a copy of the proposed amendment or amended pleading, which must be serially numbered to differentiate it from previous pleadings or amendments.

(Cal. Rules of Court, rules 3.1324 subd. (a).)

I imagine a clever opponent could file a motion to strike the amended complaint for the failure to follow court rules, but I doubt it would be fatal, and the trial court would allow this to be corrected.

Mr. Roach is correct. If the complaint has already been served on the defendant, you need to get court permission to file an amended complaint; if service has not yet occurred you do not need court permission but are supposed to have it clearly stated in the caption that it is an Amended Complaint.