I 100% agree with this. It's the centre of the case. If the defence cannot explain the deleted backdated PM cheque on the 5th, everything falls apart for them, because it proves Chase already knew Joey was dead. As you say, the problem was he couldn't delete the activity log in QB. He needed all the cheques to be created before the 5th, to fit with the story he told Dugal. Backdated to the 5th wasn't good enough. It's that greed that sinks him. And ironically if he hadn't backdated the cheques - the case against him would be far weaker.