I purchased Lenovo legion y520 at 26 Jan 2018 But laptop has sticker made in 2015 And the box of it has another. SayinhMadeIn2017forLenovoIN?

Sticker might be old, and on a new laptop.
Shell with sticker might be old, and on a new laptop MB, other parts.
Laptop might be old stock, either out of warehouse for first time, or refurbished after a return for some reason and sold as new with equivalent new warranty. If you register it or have the receipt to prove you bought it "new", you should get a full warranty period.

Laptops can be manufactured 5 years before they get marketed into your store that brand new computer on the Shelf that was shipped in 2018 could have been made back in 2015 in the manufacturing plant in China