PSA: there are two suitcases
Not a theory but none of the flairs apply.
In season 2 episode 1, Tabitha and victor find a suitcase in the tunnels. It contained a wedding dress and has stickers on it.
In season 3, episode 4 Victor reveals the BIW told him to collect precious belongings of the dead and bury them. He has this suitcase in the fort with Sara. It contained a bunch of random items (glasses, playing cards, etc.) It is different than the one in the tunnels, different design/color and has no stickers.
In season 4 episode 1, the MIY digs up a suitcase and uses the clothes to shapeshift into Sophia. This suitcase is identical to the one from the tunnels. All it seemed to contain was sophias outfit.
I noticed many people also thought it was the same suitcase. I had been thinking the BIW is bad because I thought they were the same suitcase, and had forgotten the one in season 2.