You're mixing up two different issues. One is staffmods, the other is automods.
Staffmods are the +1-3 to up to three skills. They're based on the ilvl of the item. None of the normal claws can get staffmods. All elites can. The exceptionals are divided. Those claws that can get staffmods can get any assassin skill if the ilvl is right. Refer to this topic for details. If the ilvl is greater than 24, you won't be able to get +claw mastery.
Automods are just an extra prefix some items get. This is what the Paladin shield resistance bonus is. These automods follow the same generation rules as other affixes, but they come from a separate list.
Staffmods are the +1-3 to up to three skills. They're based on the ilvl of the item. None of the normal claws can get staffmods. All elites can. The exceptionals are divided. Those claws that can get staffmods can get any assassin skill if the ilvl is right. Refer to this topic for details. If the ilvl is greater than 24, you won't be able to get +claw mastery.
Automods are just an extra prefix some items get. This is what the Paladin shield resistance bonus is. These automods follow the same generation rules as other affixes, but they come from a separate list.