Southperry & Nexon Collaborative Event

If what Lozmaster said regarding the item is correct your first statement isn't.

I was making a logical guess based on the SP database, they do still have a form of tradeblock tag, but they are tradeable until someone equips them.

For instance, all "reverse" items have this form of tag, you can trade them as many times as you would like, until you (or someone else) equips them, at which point they're permanently binded to the character.

5,000 codes and just <2000 users?

Don't take the user number as a solid limit on people participating for codes. There are a significant number of people that aren't signed up taking part too.