I sympathize. The night before our last cruise, I was gathering the boarding documents, but could not find my wife's BC. We had traveled across the boarder to Canada recently, so I was sure it was in the "safe spot" where we keep them all, so had not felt the need to check before then.
As it turns out, the BC in the "safe spot" was a hospital copy, which apparently immigration at the border accepted but
DCL said they could not.
Needless to say we were frantic and very mad at ourselves for not checking sooner. How were we going to explain to our kids that we could not go on the cruise (leaving my wife behind was not an option)?
We had no idea where to look, but we turned the house upside down for about 2 hours, and out of despiration, decided to go through the sovenier bag from our first cruise in 1999. Lo and behold, there it was! It took me about 2 hours to calm down enough to resume packing and getting ready - by then it was about 1 AM!
We now have passports for everyone (I already had one for business), and we keep them in a secure spot. We also ordered extra copies of everyone's BC just in case.
Moral of the story - secure your proof of citizenship papers the day you book the cruise!
BTW - when we got to the port, the couple next to us in checkin only had a hospital BC - they had to sign a few extra forms, but were allowed on. This was a 4 day on the Wonder - the DCL CM said they could get by on the 4 day with this BC, but the countries visited on the 7 day would likely not allow it (so they would have been turned away at the dock)!