Inventory Crafting Slots not targetable

Cannot target crafting slots in inventory with testfor command (unlike every other slot):

testfor @a {Inventory:[{Slot:80b,id:minecraft:apple}]} - doesn't work

testfor @a {Inventory:[{Slot:34b,id:minecraft:apple}]} - works

[19:41:24] Xyphon did not match the required data structure