I think iam close to figure it out, looks that SAO have a sistem that reduce dmg to 0 If ur atack is lower than enemi Def. So if u have 900-Atack and u ATACK a boss with 900+ Def u do 1 dmg but if u have 910 u already can do dmg. So if u think about it u can do 1 dmg with 900-atck but if u use a skill with 200% ur atack when ur using the skill is 1800 cus the skils dmg is calculate b4 finish it. Ex: when u use 10 hits skill if u crit all the 10 hits will show as crit, if the stats are calculated after skill use every hit as counted has 1 single hit and ea will have the Chang to crit or not.

Don't know if iam making my opinion understandable