A duplicate legendary at level 50 award

Just reached level 50 and was really excited to open a new legendary card (got only 2 missing - one from Scholomance and one from Darkmoon Faire), although, when I opened it, it was a card that I already have from Barrens. I own the card already in golden and now I got the non-golden version of it.

It doesn’t say anywhere in the reward track that the random legendaries are from the recent expansion only, so, I figured, that would give any standard legendary card that’s missing from the collection. It was souble the bummer, since I’ve got the card that doesn’t see play for the class that I don’t really play (so almost no chance to wait for nerf and get a full dust value back).

I’m fairly sure that that shouldn’t happen, since, again, nowhere, as far as I’m aware is specified that those track rewards are from the latest expansion only. So I would be happy if some feedback could be provided to me. Thank you

I don’t think it’s stated anywhere but it’s how it works for everyone.