There are a ton of things that can end up in the "Loose" category. Below are some examples with 1-3 being the most common.
1) Trade-Ins from Team and/or other trade-ins.
2) Things we tested around the shop.
3) RMA returns that tested okay but we replaced them with a new item anyway.
4) Rejects from the build-room that we didn't have time to package.
5) Random items that we simply lost the packing for and/or original packing damaged.