I'm a backer, and I'm supposed to have the black wurm pet.
I don't.
The game in my library says "+3 dlc" but I got only 2. Refreshing the page doesn't help, tried that many times already.

Why u think we should get a wurm pet ?
From my understanding its a piggy pet + healing ring item only.
The +3 dlc might refer to manual, cookbook and documentary

If you got the Kickstarter edition then yes, you should have two combos: Cloak + Wyrm (two seperated installers), Pig+Ring (One installer)

Try https://www.gog.com/account/refresh

If still don't appear the +4 DLC contact support

Does this apply to minimum backers or higher tier ones?
I got +3 DLC tag on mine and two extra installers, Kickstarter Item and Pre-Order Bonus Items and Pet. I think one DLC of the 3 is cookbook pdf and documentary. Am I missing something?

Btw I forgot to install the extra stuff and haven't even seen what they are. Are they worth anything?

You only get the Wurm if you backed at the $250 tier or higher.

Everyone else only gets the Obsidian Order Cloak and the vanilla Pre-Order bonuses.

I truly don't remember if there is difference, however this post suggest is not: http://www.gog.com/forum/pillars_of_eternity/kickstarter_items_missing/post9

By the way, the items are not important at all, are just extra good thing but don't affect your experience.

I would guess champion and royal edition are equivalent to higher tiers than the minimum.
Thank you both for clearing it up. :)

I'm so confused now, I'm a KS backer and I only got the pre-order bonuses pig+ring - should I have gotten this cloak too? Or is this too only for higher tiers?

That was VERY confusing.
Thank you for your clarification. Anyway, I think that the cookbook and manual shouldn't be referred as "dlc".
Besides, when I click on the game in my library, only 2 items are marked as "dlc". The cookbook, manual and documentary are marked as bonus content.
So, to summarize: I have "+3 DLC" on the game but only 2 are marked as dlc. I think further clarification from GOG or Obsidian is in order. I have it... so you should have it too. It's just a cape without stats anyway.

Are you sure? I am a backer and I didn't get this. I just went to eternity.obsidian.net to check what my accoutnt says and the text there is: "Includes the base game of Pillars of Eternity. Added bonuses include the Giant Miniature Space Piglet and Gaun's Pledge pre-order items." even on the Obsidian page there is no mention of it. I absolutely do not want to bother the GOG staff with questions about a cloak unless I'm really missing something.

Did you back the game on Kickstarter, or some other way? Sorry, I just realized I haven't followed your previous posts.

The cloak DLC states – "DLC: Pillars of Eternity: Kickstarter Item" – so that seems to imply all KS backers get the cloak. That said, I removed the cloak very early in the game once I found useful items. You're not missing anything there.

I backed it on the first day of the Kickstarter campaign on Kickstarter. I know 2 more people who have it on GOG and I'll ask them later if they have this item or if it's "missing" for them too.

You're right, they added another DLC.
Its called "DLC: Pillars of Eternity: Kickstarter Item ".
The pigglet and the ring are " DLC: Pillars of Eternity: Pre-Order Bonus Item and Pet".
They are both named version 2.0.0.1 and 7.7mb so I thought they're the same at first, i guess not!

Also the cloak is pretty useless, no stats so ....

You're not actually missing out on anything important. The cloak does absolutely nothing and is purely cosmetic. If you're still concerned about it, I'd suggest tossing Obs devs a message to see what they say about it.