So I've got a support ticket in for this with Rare, and I've talked with Xbox Live Support and we've figured out the problem with DLC (like the Black Dog Pack) for those of us with Multiple Microsoft Accounts (Xbox Live IDs).
If you're like me, and an original Xbox user, you likely have 2 Microsoft accounts. One when Xbox Live came out (mine was with hotmail), and then one when windows 7 came out and required a microsoft account. Since at that time hotmail was shut down, it wouldn't allow you to use your ID to sign into windows or buy windows with it, so you had to create a new one with a new email. So I've got two. You guys see me talking on my original Xbox account, but I have another one with my gmail for my PC.
I bought Sea of Thieves on my PC. So Cross-play unfortunately is completely out of the question for me. Because I have no way to get my PC account on my Xbox as my "main" account, since I have many games bought on my old Xbox account. I redeemed the Black Dog DLC on my hotmail account (this user ID I'm on), because the way it usually works is that "base games" can be shared among accounts, but DLC and addons only work on the ID you redeem them on.
Now to lay the picture for everyone - PC is logged into Windows on one account. Xbox App on PC is logged into my hotmail account (Monkeychow01). This way I can play the game with my old Xbox live ID on my PC. The code was redeemed on my hotmail account (xbox support verified). I log into the game? I cannot see the items.
If I sign out of the Xbox app and back in as my windows account (the Xbox live ID I don't use, but the one that the BASE game is bought on)....and I load into the game? Surprise, all the DLC is there. Normally (per xbox support), this isn't supposed to happen this way. The licences are applied to the Xbox Live ID, and the code is supposed to look at the ID, and not which ID the base game is associated with.
So long story short. I have a ticket in with Xbox support that they're forwarding to Rare. I've got my own Rare support ticket from the website logged to ask them to fix this. And if you are in the same situation as me? You can't have your DLC right now. It's also a MAJOR concern for those of us on PC when DLC comes out, because if anyone is in my situation (using a different Xbox Live ID than the PC one you log into), and they buy DLC directly from the microsoft store on the PC (which would be natural instinct for folks that do not know you have to buy it online through xbox.com on the ID you use to play the game), then they will never get their DLC and it can cause quite an uproar because the code will be locked to the wrong account.
If any of you are in this same situation, I'll let you know when Rare responds to the support ticket. But for now there is nothing we can do but wait for code to be updated.........
