I can't comment on the other problems, but 1261/1318 is pretty much the standard "full" set of cards. If you had positively everything, including the cards you can purchase in the in-app-store and a handful of special promos that pre-date the steam launch, the most you could possibly have is about 1270.
The 1318 number has always been a little off. It includes a bunch of unreleased cards that the app knows about, but aren't officially part of the game yet.
That's interesting to know about the 1318 figure; thanks for that.
Still, the Obsidian Edition is supposed to include Eder, Pallegina, and Goblin Golem of Obsidian, all of which aren't included in the Epic/Legendary DLC. Unfortunately, I don't have those three in my collection, unclaimed tab, or showing anywhere in the store.
There are also three "Legendary Items" mentioned separately from the batch of treasure cards that the previous DLC unlocked, though I'm not sure whether that's some sort of error in the Obsidian Edition description.