All you need to do is verify from the RMV that the duplicate CR has been legally obtained. If there's another vehicle with the original CR, they will be in trouble, not you. No one can be 100% certain that there won't be another vehicle with the origin CR.
At the same time, if you buy a vehicle with an original CR, no one can be 100% certain that there won't be another vehicle with a duplicate version of the same CR. Get the documents checked. That's the only way.
Thank you Crosswind....