I would say so. As long as it doesn't have something wrong with it. I bought a Strix GTX 970 on Ebay and it had a clicking noise with one of the fans. I was able to RMA it because it hadn't been 3 years on the warranty and the GTX 10 series wasn't out yet. No proof of purchase was necessary. I simply said the date of purchase was the date I bought it on Ebay. :/
But if you can RMA it that would be great. Not sure how that would work since they've been out just over 3 years.
Overclocked the GTX 970 is as fast as a GTX 1060 6GB or GTX 980.