it's not coz some shadow equips already have that description like alchemist armor will give you atk+100 at +10 with learning potion skill and same with bard/dancer shadow shoes.
Oh, nice. Didn't know they gave that much atk, their description doesn't really mention the number. Pretty stronk
ATK가 러닝 포션 레벨만큼 증가한다.
제련도 6 초과시, 초과한 제련도 1당 ATK가 러닝 포션 스킬 레벨만큼 추가로 증가한다.
ATK increases by the running potion level.
When the degree of refinement exceeds 6, the ATK is increased by the skill level of the running potion for each excess refinement level.
It seems like it give bonus atk from + 7 to +10? Which means 10 + (4x10) = 50