Just because you bought it 3 years ago does not mean it was made 3 years ago. It is not uncommon for many big stores to buy guns by the truckload to get a good price. It could take years for them to sell them all.
Several years ago I bought a Marlin 336C 30-30 from our local K-mart. The price tag was about $100 less than they were asking for one of the birch stocked 336 A's. When I looked at the SN, the gun was 11 years old.
When I asked about the 11 year old gun I was told that K-Mart had recently stopped selling guns in California, and all the old stock from there had been sent to other stores across the country. It still had the 11 year old price tag on it.