Vanguard Amory - How does it work?

I am a returning player who quit after TFS. So much has changed. I got Edge of Fate and worked through the campaign with my Hunter.

I got a couple of pieces of Armor from Zavalaa called Vanguard Amory. Very high stats. But after that it has said I have already had a piece this week. I am sure it has been longer than a week it says that, but maybe I am mistaken.

Now I have started logged in with my Warlock and I get the same message.

Is it only one piece across all characters every week? Or are there other triggers?

Thanks