Careful critical analysis of Lisa's statements - i. e., exposing them as lies - go a long way to cracking the case.
Your point may be true, but unprovable based on publicly available information. Hugh was simply showing that the government's own reports are not supported by the government's own documents. At times, the government's own documents make outright deceptive statements in light of the government's own documents.
I’m thick, I know, but I don’t understand what could have come to light that would preclude Lisa getting these things, the insurance money, and the oil leases that would have been rightfully the family’s upon Vince’s death. They were married, legally, living together as husband and wife. She wouldn’t get life insurance if her name wasn’t in the spot marked “beneficiary” but I’m pretty sure it was. What would have prevented her just claim on these things? Nothing comes to mind, and I have a good imagination.