New Redemption Grab Bag now includes an assortment of 500 cards from five (5) different expansion sets. Available at Cactus website.
The RoA fortresses can hold characters, but never mention when you can put them in/remove them, so they default to the prep phase.
For most fortresses, where you can add/remove characters more or less at will, you're restricted to the prep phase. The RoA fortresses can hold characters, but never mention when you can put them in/remove them, so they default to the prep phase. I don't think Tartaros is subject to that, though.