I have the same issue I had last time, this time I have a double drop of a IB helmet and a Mercenary hat that a few months I bought already and later after opening 100 Commendation Chest.
Before the Shilling buying system this didn’tn happen to me. Back then when I had all the hats those from another random character dropped. In this case I was opening all my chests with Bardin Slayer and I got first an Irobreaker Helmet and after that a Mercenary Hat.
Seems like the drop table doesn’t update properly when you first buy the old hats, but that’s just my guess.
Although this thread is marked as acknowledged, maybe it would be better to submit a Support Ticket instead. The Support Sharks got back to me about this same issue in just a few days after I made the request.