I’m hoping to get some clarity/official answer from the game makers about this one if possible.
All starter weapons keep the same damage die and just go up +3 with each Tier. The Dualstaff is the only exception. It goes up +3 but ALSO increases its damage die from a d6 to a d8? I am wondering if that’s just a typo that hasn’t been noticed yet or if for some reason this weapon is more special than the rest and gets a double boost at Tier 4.
That’s how it is printed in the most recent update of the book, so it’s an issue to take up with Darrington Press. Demiplane is just a distribution platform, and does not have any control over the content they have licenced.
There is an errata feedback system, if you would like to make Darrington Press aware of the issue: