My guess:
Weapons (old): my best guess would also be /bonus (preorder etc) weapons. I highly doubt that e.g. swamp club will be returned. This is way too specific and I doubt in the OS knowledge of current anet employees.
I actually think it could be the opposite:
Those few nerfed drops don't require that much special knowledge. It's a few skins that you can easily find out with a little research (if thats even necessary in the first place, we're talking about the company that created the game) and thats it.
Pre-order items on the other hand would set kind of a weird precedent: They are items that you could never get from gameplay, tied to buying a special version of the game. First of all they would kind of compromise the sales of the (admittedly only really remaining single set of) bonus items you can get on their online store. And second, where would anet draw the line? It would be arbitrary if not ALL of the bonus weapons were added. And then why stop there and not make the divine aura available for everyone or make mini kuunas earnable in-game.
I'm not arguing for or against it, i just find there to be issues with that logic unless we flat out get everything that's ever been a bonus code.