Help I think I was duped by seller iPhone 4

So, I bought a used iPhone 4 from the internet. The seller said he bought it April 2011 but got a replacement from Apple on January 2012. When the phone arrived, I noticed that the IMEI sticker had been peeled off. So I couldn't check whether the phone IMEI was different or the same (obviously if it's a replacement phone the IMEI would've been different). Then I checked the serial number to know the manufacture date. 79******A4T. it means the phone was manufactured on the 12th week of 2011, right? So I suspect this is the original phone that was bought on April 2011, not a replacement! What do you think?

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