I have an existing Series3 with Lifetime Service. I'm thinking about upgrading to a Premiere. TiVo's website says I can get a MSD to reduce the Lifetime from $499 to $399. But what would happen if I sold my Series3 and the new owner obtained the Lifetime on that unit? My other Lifetime would already be paid for at $399. Is this legit? Do I just have to have both units on the same account the moment I buy the new, discounted Lifetime?