USA - early prescription filling and postdated prescriptions

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Hi, this thought occurred to me while posting in another thread in another forum (about ambien), but I realize the question is better placed here.

I know that you can refill prescriptions early (I think it depends on which schedule the drug is, though), but I'm wondering about postdated prescriptions?

I've had ambien (sechedule IV) refilled 10 days early (20 days after original fill). Could this mean that I can fill my post-dated prescription up to 10 days early?

What about other schedules?

Thanks