A friend of mine lived with her partner in his place for 13 months. They did not sign any contract with the owner. Now they want to provide evidence of they lived together for sponsorship application (outbound). The owner is willing to help. The owner offers to sign a back dated contract and it will be notarized but the stamp will show a recent date. Is this ok? What else can they do to prove that their contract is real (not fake)? Any suggestions?