Was his housekeeper ever on the witness list? If willing, she could have easily testified as to whether this damage was preexisting.
A forensic expert should also be able closely approximate the width of the object that caused that dent. Perhaps the same width as a cricket bat...
ITA it also works to leave it as a glaring unanswered question in the Judge& assessors' minds.
I am not 100% sure but I think the damage panel may have had traces of the metal copper on it and I think a states witness said it wasn't the cricket bat.
Also I am very surprised Nel didn't call the cleaner lady or Frank to testify about the panel .
In the past I have just tried to accept the fact that Nel knows best and if he thought the staff could shed light on the case and help I am sure they would have been subpoenaed .