I understand exactly what you're saying.
The items aren't in 100% chronological order down in your scroll bar with the pictures. Like items pair up. You're getting all your items, you just have to scroll further over.
For instance if the first item your dweller earned one hour into his/her wasteland expedition was a Formal Wear outfit and 2 days and dozens of items later your dweller finds his second Formal Wear outfit, it won't be the latest picture in your scroll bar. It will be back at the beginning paired up with your first Formal Wear outfit. Does that make sense?
So if your dweller earns in chronological order:
Rusty Pistol - Enhanced Shotgun - Combat Armor - Rusty Pistol - Battle Armor - Enhanced Shotgun
In the picture scroll bar it will look like this:
Rusty Pistol - Rusty Pistol - Enhanced Shotgun - Enhanced Shotgun - Combat Armor - Battle Armor
Follow?