The notion of court orders nunc pro tunc is a very vague equitable doctrine.  Even if counsel obtains a nunc pro tunc order in criminal court, there is no guarantee at all the immigration court will reach the criminal court’s conclusion that the order or plea was entered on the backdated date cf. United States v. Esparza.  The immigration courts generally follow federal immigration law on these questions, rather than the vagaries of the law of the 50 states, because of a desire for national uniformity.