The passes are upgradeable. Since they are MYW tickets from 2006 you can upgrade them within 14 days of their first use and will therefore be able to upgrade them to cover your whole trip.
From what I understand, complimentary tickets are not upgradeable.
Now, on to a different angle unrelated to what I just quoted ...
Please allow me to clarify what I said in my earlier post, lest anyone not quite understand.
Let's say the OP will be going in October and will go to parks for 6 days. If the OP uses the free 3-day pass, he/she will still need to buy a 3-day pass per person, in order to have park admissions for 6 days. A 3-day park hopper will run about $264. At the end of the trip, the OP will have no park admissions left.
So let's say the OP holds onto the free 3-day pass and instead buys a new 6-day park hopper. That 6-day park hopper will cost about $279. AND the OP will still have a 3-day pass to use at any time in the future.
Do y'all see what I mean now? If I use the free pass now and buy an additional one, I'll spend $264 with nothing left but memories of a great trip.
If I just buy a 6-day pass now, I'll spend ONLY $13 MORE and have memories of a great trip
AND a 3-day pass in my pocket to use any time in the future.
Make sense?