I think that the "+" for weapons is for OB.
What happens is that when you use the parry option, you allocate some of your OB to DB, doesn't matter where the points came from.
For example, you have +30 OB with your long sword. +10 from ranks in long sword, +10 from stats, and a +10 for the item (long sword +10 non magical).
You can allocate this OB anywhere you like because all the bonuses enhance your OB.