Well the product's warranty starts with the manufacturer when it ships out from them down the supply chain. The warranty starts going on the product. BUT when you buy it it could have been, usually is resold 2 times at least between distributors, shipped half across the globe and stuck in storage of a shop, say 6 months have passed since the manufacturer last saw the card when they sold it but for you you only see it today and for you the shop, distributor, I don't honestly care who, offer say 3 year warranty. Problem is who ever is going to claim warranty with the manufacturer has it running 6 months earlier than you. Of course some companies have their own distribution and service centers etc. so the middleman resellers are fewer and this warranty time not as big always.
But you can still run into this when you return in warranty at the end, the company that bought it from the manufacturer doesn't have the warranty anymore on it with the manufacturer and they try to sweep it all under the carpet so they don't have to eat that cost of the card as a loss. But by law in most developed countries you do have warranty, they don't, it's their problem, not yours, but they may still try to put it on you to eat the loss instead.
It used to be quite normal years ago that when product was not made anymore but still in warranty they would upgrade you to a recent or at least more recent product that they do have. Say RMA 280x now, get a decent refurbished or new 380x back, sure I wouldn't expect RX 480 new since it just launched and they probably have some left over 380xs. Still this is how it should go, if they cannot replace with the same working product they should either upgrade you free of charge or give you money back.
It's always a big hassle to return anything as it's not up to the shop what you get but up to who ever they bought it from.
Unfortunately finding the necessary laws and such to know how it is precisely in your country and what your rights are to the letter is almost impossible. Unless you know a lawyer or own a shop and the shop has a lawyer then you most likely won't find out.
I've had warranty on my 280x until April 2017, now what they've sent me back it says 24 months, so until end of June 2018 and it's pretty much DOA. Too bad I don't live next to the shop so I can RMA it for free, but I gotta send it to the shop which costs me
Otherwise I would happily RMA every damn crap they send me until they finally get it right.