I can fit 1,000 rounds of 5.56 in a single 50 cal ammo can, but only if I remove it from the cardboard boxes. Same applies to .45ACP. I can also fit 1,000 rds of 9mm in a 30 cal can.
Only ammo that I buy in bulk (500 or 1,000 rd cases) do I separate and store in Ziploc bags. #1 reason is so the full 1,000 rds fit in a single container. #2 reason is because I also read/heard that the cardboard can absorb moisture. I use desiccant packs to remove the moisture. Why put something in the can that might add it back?
Some ammo I buy comes in 100% bulk packaging -- a plastic bag inside a cardboard box. No smaller boxes at all. Other times, bulk ammo comes in cases containing smaller 50 rd boxes. The 5.56 Magtech CBC 50rd boxes have no dividers, so all you really get is the ammo divided by 50rd units and the same minimal stamped info: ammo type, lot number, and not much else.
I always keep ammo from each bulk case together. I also remove the bulk label from the exterior box or the end flap from a couple of the smaller boxes if that's how they were packaged. I place those in their respective ammo cans. That way it's not just "my word" on what's in the can.
I use the Ziploc bags more as a convenient way to count what I take out or have left. Not sure it adds any more protection. I will write the caliber, brand, type and amount on the outside of each Ziploc bag, just in case a bag wanders off from the storage can.
If you're concerned about ammo you want to buy, you should examine the case headstamps. I'm sure the seller would be okay sending pics of whatever markings are on the "loose" rounds. If you aren't sure what the markings mean, the info is easy to find online.
My .22 ammo is in the original boxes inside ammo cans. Most of that is CCI MiniMags, so the boxes are plastic. The rest is kept in their cardboard boxes for organization -- so I know which is which.
These are my general rules for my ammo. Not saying it's perfect, but it works for me.
If you think about it, aren't you also having to trust that the ammo in a retail box is what was originally in it?
