I don't know if you have to have both tags but I can tell you that it won't hurt to have 2 tags on your bag, there is always a chance one can come off (I have lost many tags over the years). I also put identification inside my checked bags for that same reason, I put my name, address, cell phone number on it along with other pertinent info that I feel is necessary which depends on where my trip will be. A locked bag can be opened and if the information is in the bag, it can be returned to its owner. I have to say that I have only had 2 "misplaced" bags over 35 years of traveling and both were found and delivered to me, one was sent on another plane due to weight restrictions on the flight so lots of people didn't get their bags, the other time I filled out the lost bag form but in the meantime when the bag was not collected in a timely manner at the wrong airport where it had been sent, they had opened it, found my information, contacted the proper airport and it was delivered to me the next day at my hotel.