What is the effect of an ex post facto violation of the formerly applicable sentencing provisions in a sexual assault case?

Where the evidence at trial does not establish that the charged molestation occurred on or after the effective date of the statute providing for the defendant's punishment, the defendant is entitled to be sentenced under the formerly applicable sentencing provisions. (People v. Hiscox (2006) 136 Cal.App.4th 253, 256.) A claim that an ex post facto violation resulted in an unauthorized sentence is not forfeited by failure to object in the trial court. (Id. at p. 259.)