I thought that was talking about the golden version. You know, in the visual guide to the anime, how Nasu points out that IA is like a 80 and Golden Excalibur is like 1000.
The point is that the weapon alone without putting mana into it and calling its true name is separate from the activated NP and implied to be probably ranks lower in general attack power except for some cases like Vasavi Shakti.
If you went by D&Dish terms, you could probably think of it like
Regular Excalibur without injecting magic energy in it: STR damage
Invisible Air: +10 bonus damage
Golden Excalibur: +10d6 damage
Excaliblast: +10d6 damage, 3 squares wide 50 square line AoE
If you actually had A ranked STR and you hit Berserker, you'd be able to hit him with STR damage. If you hit him with it with IA over the sword, you wouldn't gain any of the IA bonus damage because IA is not an A-ranked NP. If you hit him with Golden Excalibur or Excaliblast, you deal all the damage and win all the experience and treasure forever.