I agree with this assessment. It could very well be listed on another site and purposely not listed with GC.com. It could also have been cross-listed to GC.com and has not yet been approved or was denied but it is active on another site. Simply removing it without knowing is a bad idea.
He-he. When I saw this post, I thought I was on the wrong website.
Yes, lots of excellent ideas here, including NiraD's that I never would have thought about, someone could have "thrown down" a replacement. I dunno, are there any previous finders with more than 5,000 Geocache finds? Just kidding, forget that. But we definitely need more information here, most notable which of your finds this happened at.
This letterbox was found near Elder Bridge Treasure, GA.