the stats on a spell/combat art can change depending on who is examining them. this is normal.
As is that the stats are based on a mob at your level.
so even though dmg is 100-500. but you are going against something a level above you.
the actual stats which you don't see in the examine would be 50-400.
the info is based on you and a mob at your level.
This explanation is over simplefied; you can search the forums for more specific information.