Verification methods and tools developed so far have assumed a very simple model of rule-based expert system (RBES). Current RBES often do not comply this model and require more sophisticated verification techniques. A RBES model including uncertainty and control has been used to analyze four verification issues (inconsistency, redundancy, circularity and useless RB objects), identifying a number of new verification problems. The concepts of labels and environments (deKleer 1986) have been extended to incorporate uncertainty and control information, obtaining the constructs extended-labels and extended-environments. They have been used to express and solve these new verification problems.