I had previously purchased the motu expansion, and received and used the greater heroic exp tome that came with it. After searching around a bit and finding no notification that the epic version overwrites the heroic version, I bought and used the greater epic exp tome. There was absolutely no warning in the store of this, or when I used the tome. In fact, on multiple places in the forums it says that they don't overwrite each other. Yet when I did use my new greater epic exp tome, it had removed my greater heroic exp tome. This is confirmed by the conversation I had with a GM about it.
Some clarification on this would be wonderful, thanks.