I agree, it is somewhat strange, but as Wolf suggested, they would merely not have had the chance to formly 'study' the art, instead picking up bits and pieces along the way (doubly so if they have secondary insight / Elementist)
As an aside, with those suggested L,Q, they all fit within the suggested customized covenant creations rules from RAW, which is a bonus 
Kal
My imagination came up with the house rule for this that says, when opening arts, roll a D6-1 for each art and see what you start with(or if you prefer not to be so random about it, get 2 each of score 0,1,2,3,4,5 and another 1 each of 1,2,3 which is minimally below what average rolls would give and adds up to 80XP, wether you want to discount these xp from apprenticeship xp is optional(we added it for simplicity´s sake))...