I think its just that baseMagicLevel is ur basic mlvl with no attributes that increases this skill. (With 100mlvl and spellbook that gives u +3mlvl its still 100 (base) )
MagicLevel is all urs mlvl with items etc. 100mlvl +3 from spellbook = 103
Its all the same with others stats ( baseskill, basespeed, basemagiclevel )
example:
local min = (magicLevel * 4.75)
local max = (magicLevel * 11.5)
With BaseMagicLevel 100 ( +3 with spellbook ) u can deal max 1150 dmg
With MagicLevel 100+3 u can deal to 1184,5 dmg
/Sry for bad eng