We returned from a 5 day trip to Vancouver a few days ago. There were 5 of us using public transportation, so we had 5 Compass Cards. No where in my reading while planning this trip did I read that you can't get a refund for the $6 card deposit and any remaining funds if you don't have a Canadian address with which to register each card. All I read was that you could go to a specific location in Vancouver or mail them back later. The Vancouver location didn't fit our plans, and since I thought I could mail them back for a refund I didn't make any special effort to get to the location for a refund. I called today and was told, sorry, no refund without a Canadian address.
So, warning to non-Canadians who don't have plans to return to Vancouver or who don't have a Canadian friend/relative under whose name you can register your card (they'll get your refund and have to send you the money)...get your refund while you're still there. It's not a life shattering amount of money, but it would have been nice to know this ahead of time. There's nothing that I saw at the kiosks (or here on Trip Advisor) that explained it. Maybe I missed it.