I am confused, it happens.
Which statline does the Accursed Crozius present in the Tome of Excess? Possessed or non-possessed? It does have a rather powerful statline for a one-handed melee weapon and Felling (4), which from it can be argued that it is the possessed one... by the same token it is mentioned that it is a Power Maul/Mace which has a base of 1d10+6 Pen 4, add in the Daemonic stuff and it would be put at 2d10+11 Pen 9 so that doesnt fit either... Of course add in the daemonic bit on the statline in the book would make for one imba weapon - 3d10+11 Pen 12 Felling(8), nasty stuff.
Of course the statline for the Lash of Torment and a few weapons in the Tome of Blood doesnt follow the normal rules for Daemon Weapons either... sooo?
Personally I tend to favor Legacy weapons anyway... less chance of an ornery daemon killing the rest of the warband in their sleep.