Hmmm,..
Here in N/A, we use Till receipts as Proof of purchase(POP), no warranty card to speak of other then that.
If you can prove you own it, and where you bought it, that usually determines your warranty eligibility.
Usually, once a phone is sold, it is covered by the carrier an the manufacturer to a point, the carrier may swap a unit or refer it back to the manufacturer and still swap a new unit to the customer.
However, in this case, your looking at, Someone else buying one and selling it to you, then you would prob get the till receipt and if you needed service would be directed to send it to a authorized LG outlet/dealer type of thing, as it's no longer being used on the carrier it was meant for.
So, what you need is "POP" Proof of purchase, it will show the date an location on it and will allow the manufacturer to determine if, there is a warrantable product in front of them or not.
So if one is sold to you with a (POP) you may be able to get it serviced under warranty if needed at a LG outlet, if no (POP), You would be responsible for all costs.
Last thought, Phones, Cell phone, are a pretty personal item, there are many levels to one, from it working correctly out of the box, to did it have a shortcoming the manufacturer ignore or not etc... Then you have what is ever happened to it since it was removed from the box to contend with as well in buying one second hand. (Then if overseas, get it shipped back to a authorized repair depot an damages out of pocket if they decide not to cover the warranty)
To be honest, I have refused phones, where the dealer takes it out of the box originally, I know I am twisted, but if someone is going to break it in, I AM.

I respect fellow like yourself that search out a phone like this, I do, though if you can afford it, buy it new off of a dealer/carrier that will ship it to you, an BE covered with a real POP in your hand.
If second hand imo, All bets are off.
JMTC
Peace
WR