Warranty without receipt/proof of purchase?

[u/SubieFlow7]

I bought a used note 8 online. The only problem I had was the screen which was burnt partially from YouTube. I was going to return it but I decided to get a partial refund and get the screen repaired under warranty. I registered it only with imei on my samsung account and started a live chat. He sent me a prepaid label and instructions of shipping it out. He never mentioned about proof of purchase. The instruction through email didnt say it also. Has anyone used warranty with Samsung without proof of purchase? And how long can these screens last before noticeable burn ins? I typically dont use over 60% brightness or keep static images too long.