According to yesterday's Presentation by Mr, Marsal...many of the 64,000 claims are from Lehman Program Securities (I believe almost 40%). These are items that are on the liabilities side of the balance sheet in various forms, IMO.
Also, some claims are from the deriviatives side and have yet to be settled, priced and terminated properly. These will net out according to A&M in favor of LEhman currently. However, that does not stop someone from filing a claim. If there is no claim by now, it has been lost forever.
Coach T