That new MBP that was given to you now only has a 6 month warranty for the remainder of the original AppleCare you purchased. So, basically, AppleCare cannot be bought for that new unit? Yet if you take the refund of the remaining 6 months of AppleCare, you can buy AppleCare again for the new unit that was given to you?
No.
Wait.
Apple is known to handle the situation in a variety of ways depending on the manager; i've seen the following on these boards:
1. Apple gives you a new machine and renews Applecare for 3 years (crazy, I know).
2. Apple gives you a new machine, resets your Applecare, but doesn't refund the prorated amount of your previous agreement.
3. Apple gives you a new machine, resets your Applecare and gives you a prorated refund.
4. Apple gives you a new machine with the duration of your previous agreement.
I've gotten to experience '2', but there are some active threads going on right now that describe '3'. I've seen '1' very infrequently. I've seen '4' just a couple times as well, but more than '1'.
I have never seen an offer to choose between a prorated refund and/or adding it to the new 1 year machine warranty *but* i'm not saying it doesn't exist.