DexCool was not designed for pressurized closed systems, but instead for the conventional systems in our trucks which are not a true closed system (see non-pressurized overflow tank). DexCool does not like to be run low and have a lot of air in the system which creates an acid. Then again, conventional green coolant will do the same thing but is more tolerant of being run while low on coolant before it creates acid.
GM recommends adding an extender to DexCool after two years IF the coolant is clean. I'm not aware of any coolant that doesn't recommend the same thing after two years, even the long life coolant.
In either case, changing out the coolant every couple years addresses any of the potential problems by any of the coolants on the market. I end up working on my trucks often enough and having to dump the coolant out so I just use SuperTech.
Between my four pickups and two vans I don't think any of the coolant in them is more than a year old.......