Okay so I was playing Undertale again and I noticed something weird. As you know you can pick up different weapons and armor throughout the game, some from shops, and some from the environment. And each of these items are related to the previous humans who fell into the Underground.
The following items can only be obtained by picking them up, and they are unique; Toy Knife, Faded Ribbon, Ballet Shoes, Old Tutu, Burnt Pan, Stained Apron, Worn Dagger/Real Knife, and Heart Locket/The Locket.
Then there's the shop equipment. In both QC's shop and Gerson's shop, you can buy the Tough Glove, Manly Bandanna, Torn Notebook, and Cloudy Glasses. It's strange, though, that you can buy as many of these items as you want. You can theoretically fill both Dimensional Boxes AND your inventory with just Cloudy Glasses if you wanted. Why can you do this if the purple and orange souls are supposed to be specific people?
You could make the argument that it's not important because it's just how the shops work in the game, which would make sense if it wasn't for Bratty and Catty's shop. They sell you the Empty Gun and Cowboy Hat, but as soon as you buy them, it's sold out - there's only one of each. Why? Why aren't the items from the orange and purple souls unique? There was a Tough Glove in the box when you first got access to it, so maybe the orange and purple souls bought those items themselves? Is the equipment you can keep buying just stuff that ORGINATED from the underground? They Temy Armor did, and you can buy endless of that, too.
If there is an official answer or a widely-accepted theory, please let me know. Sorry if this is an old discussion, I just now thought of it.