Hmm... well, a person says he sent the documents and the recipient denies by saying that the documents sent were incomplete. They cannot deny by saying they never received anything because the receipt is proof that an envelope was sent. Whether the envelope was empty or the documents sent were incomplete is an issue on which evidence is then led. Based on the evidence, the court decides in favour of one party or the other.

I'm sure this point which you have raised must have been raised in the past before as TCS has been around for a long time. The courts must have set some guidelines which helps them determine what to do in such cases.