best way to figure out the whole collectible thing is to review the posts in the GC forums.
My understanding is that if it is collectible, only the owner can add this to their collection. that way it is not on their inventory list but on a collectible list. Not a huge thing if you only have a few coins/bugs but if you have tens to hundreds of them, to have them listed on your inventory every time you log a cache can be a bit much.
Disclaimer : Always answering to a higher power.
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