From bringing cars back and forth both ways,I've found the border officials only check the dash VIN to confirm that it matches the number on the title/registration and if it does,it looks a-ok to them.I doubt any of them would know what a fender tag even is,never mind cross reference it with the VIN on certain years of old Mopars.
Going by what Tobias has indicated,the dash VIN would be the one that matches up with the BC paperwork so it would be exportable to wherever and insurable and only a knowledgeable Mopar person would know that either the VIN or the fender tag has been changed.