You'd think but no. You could set the case for trial (giving up any and all chances to plea bargain for something other than a conviction), then hope the DA doesn't notice the error prior to trial. (The DA can amend the indictment any time up to the start of trial--so if you point it out, they'll just fix it.) Even if you make it that far, it's not the kind of fundamental error that requires a reversal.
If you have been indicted on a felony, you need to be discussing this case with your attorney. If you don't have one yet, start interviewing people as soon as possible. Most of us offer free consultations.
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Does the date matter? Short answer? Not usually. Why? Because of the "on or about" language that comes before the date in almost every indictment. When you see"on or about" such and such a date, all the prosecutor has to prove is that the offense happened before the indictment was done by the grand jury and not so long ago that the time limit to bring the case (meaning the "statute of limitations") has passed.
My suggestion is that you have a competent criminal defense lawyer review your indictment to see if it contains the "on or about" language and to see if it has any other errors that might be used to help your defense.
Answers on Avvo are for general information purposes only and should not be relied upon as legal advice. No attorney / client relationship is created by providing this answer. For specific advice about your situation, you should consult a competent attorney of your choosing.
A superseding indictment could correct the error if the prosecutor smells a technicality defense. I agree with my compatriot that the on or about language provides some protection from this mistake. So, a small amendment to the indictment would hold no prejudice to the defendant. Take Care!