I need help in regards to the Robbie Laidlaw bounty in story mode.

I'm in Epilogue 2 and I can't pick up the envelope in Old Harry Fen. When I go to grab it I get the message: "You can't carry any more of this item." I 100% captured Mark Johnson some time ago as Arthur, and I apparently already have the "Family Photograph" that you find under the floorboard. I can view that in my satchel under "Photographs." I looked it up and I know that the envelope is the newspaper article "Slave Catcher Newspaper Scrap" but I don't see that in my satchel under "Newspaper Scraps" so I must not have that yet. I've also looked everywhere else in my satchel and can't find it, so I don't understand why the game thinks I already have one.

I'm 99.99% positive that I didn't capture Laidlaw yet, so I'm stuck. I've looked and can't find any record of anyone else experiencing this. Did I get him already and just have no memory of it? If so, why is the envelope still there? Did I try to pick them up in the wrong order or something and cause a glitch? Any thought are greatly appreciated.