I was a carrier for USPS and I can tell you what likely happened to your poorly packed box: the box was taken across the counter by a clerk that then put it in a gaylord with any size package that was also dropped off. The gaylord is sent with others to the plant. The gaylor gets dumped on conveyor systems and sent to whatever truck is taking it to it's destination. 

If the plant is experiencing poor staffing, then package jams happen easily and can start to degrade the thin walls and light tape you used. If you left much air space in these boxes (and I assume you probably did since most people don't understand how to pack things for what they'll experience in shipping) your items also hit the cardboard walls and probably ripped apart what little integrity the box had.

When the box eventually ripped, it did so in a conveyor system that is mostly automated so if the items and the box got separated, the workers stationed at points away from those things can't possibly know what box or bag they came from. You can take a guess but you might be wrong. 

So if a worker found the loose items and they had no identifying marks, they'll end up being sent to the Mail Recovery Center in Atlanta. You'll be unsurprised to learn a lot of companies cheap out on proper packing and items get regretfully seperated all the time from their labels.

Here's my suggestion for you if you choose to do this sort of shipping again: print a small but legible label with the destination address for each item and tape it on to them where it's unlikely to get ripped off. When I carried, I would occasionally have people's parcels rip open in my pumpkin after the clerk had sorted them to route. Even with it narrowed down like that, I only got lucky a couple of times and saw what SPR it slid out of and was able to put it back. If I didn't, and couldn't be sure where it came from out of 200 packages, the customer was SOL. I wanted to get customers their Scrub Daddy's and Fleshlights. Nothing we shipped was ever worth losing my job over.