Originally Posted by
rc408
What I found was that I could use multiple cards for the same order that were issued to the same MyPoints account only.
OK, but the OP asked specifically about Amazon. That policy does not apply to Amazon. Amazon gift cards have a code on them that can be redeemed online... it can be redeemed by anyone, as the codes are not tied to a specific account until redeemed. Once redeemed, the gift amounts can simply be "bankrolled" until spent, so you don't have to actually spend them immediately (which is good because the cards are easy to lose).
So, to the OP: yes, you can combine as many codes from as many cards as you want, simply by redeeming them to your account.