My orthodontist told me I would get my braces off earlier than expected is this normal? Or will it be pushed back?

I got my braces on October of last year and my orthodontist said it would take 2 - 2 1/2 years to fix but when I got them tightened last week they said I only had 9 months left in my treatment which wouldn't even be 2 years. I'm just confused???

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