Italian to English Bus/Financial Accounting

le garanzie di bilancio differiscono dalla responsabilità legal per manmcanza di qualità delle cosa venduta. Esse normalmente coprono le insussistenze di attivo e le sopravvenienze passive che si manifestino entro un certo termine (lungo)

financial statement warranties differ from legal liability for lack of quality of the sold item. Such warranties normally cover the non-existence of assets and contingent liabilities that arise within a certain timeframe,

I'm not an accountant, nor professional translator (am checking the translation done by an agency), but I have doubts about

"le insussistenze di attivo e le sopravvenienze passive "

I've checked other entries on Proz.com, but nothing seems to quite hit the nail on the head....

All help much appreciated!!