According to the Draconic Bloodline, contained in the Core Rulebook, at 3rd level, the Sorceror gains a +1 Natural Armour Bonus (as well as resist 5 to the energy type of your dragon colour). This increases to +2 at 9th level and +4 at 15th level.
The Wildblooded Archtype states that: "When creating a wildblooded sorcerer, select an existing bloodline (such as one from the Core Rulebook, the Advanced Player's Guide, or this book), then select one of the following mutated bloodlines associated with that bloodline. Use the normal bloodline's class skill, bonus spells, and bonus feats, and the mutated bloodline's bloodline arcana..."
Linnorm - Bloodline Arcana: "Whenever you cast a spell with an energy discriptor that matches your linnorm bloodline's energy type, you gain a natural armour bonus equal to the spell's level for 1d4 rounds."
My question is this: As written, would this mean that whenever you cast a spell that had the matching energy type, you would LOSE your natural armour bonus granted by the Core Draconic bloodline and replace it with the effect from the mutated bloodline, or would the bonus from the mutated bloodline effect be added to the base bonus provided by the Core bloodline?
EDIT: I have read through the whole of the "Does Natural Armour Stack?" thread, as well as looked for the FAQ/Errata. I THINK the answer is "yes, the bonus is increased", but I'm paranoid about perfection.
You take the highest, whichever it is. Technically, they overlap.
Named bonuses of the same type do not stack unless the effect says so. Neither of these say so.
They don't stack, but they also don't negate each other so if you cast a cantrip, you keep your regular draconic natural armor