There isn't really a definitive way of ensuring that you haven't missed a document. My only advice would be to read as many threads on this forum as you can, and you will get an idea of what others have missed in the past. As long as you took the time to read the document checklist carefully and uploading something into every spot that matched the description, you have done your part.
If you do find that you forgot something, your only hope would be to use the Case Specific Enquiry (CSE) to upload the document. But there is no guarantee that it will be accepted.