In a motor vehicle accident case, is a plaintiff entitled to a supplemental complaint?

4 The insurance companies point to another passage from Radar v. Rogers, supra, 49 Cal.2d 243, 247, 317 P.2d 17 as stating: "[A] supplemental complaint cannot aid an original complaint which was filed before a cause of action had arisen. Here there was a cause of action when the original complaint was filed. That cause of action accrued when the accident happened. Every fact essential to state a cause of action, at least in the absence of a plea in abatement, is well pleaded."