Ok, so I already have the base game and an active subscription.
If I buy Stormblood Collectors edition, I only get Stormblood Collector's items and no Heavensword Collector's items.
If I buy the complete collector's edition, I get all Collector's items from base game through to Stormblood.
My question is, seeing as I would be applying this complete collector's edition to an already existing and active base game account, what will happen?