Just upgraded my 13 to a 17 and when I was looking I saw a TON of rams from Canada, some of them marked down to reflect that but most were priced the same as any of the other ones with no mention of the warranty not being good. Definitely something to look out for when buying these used. From my research I found it's only Chrysler vehicles that have this problem, and it was something Chrysler implemented somewhere around 2001-03 IIRC.
I tried asking some leading questions to some of these dealers to see if they would come out with it, none of them would unless asked point blank weather the warranty was good or not. Also noticed several dealers which had all of their used Chrysler vehicles from Canada, buying them much cheaper no doubt and then selling them at full price, screwing people over in the process.