Using the Developer Console as System Admin:
The result of this query: SELECT Id FROM ContentDocument
does NOT contain the row returned from this query: SELECT Id FROM ContentDocument WHERE Id='069xxxxxxxxx'
I've also tried ContentVersion.ContentDocumentId queries - also no luck.
The Salesforce UI does show that record to me (I can upload new versions for example).
Is there a better way (Apex) to get all ContentDocument records?